"In this lies piety: not doubting the God-bearing Fathers.” - St. Gregory Palamas

Source: On the Direction of the Ecumenical Patriarchate in the 20th Century — Classical Christianity

"Nor may men destroy the hair of their beards, and unnaturally change the form of a man. For the law says: You shall not mar your beards. For God the Creator has made this decent for women, but has determined that it is unsuitable for men. But if you do these things to please men, in contradiction to the law, you will be abominable with God, who created you after His own image. If, therefore, you will be acceptable to God, abstain from all those things which He hates, and do none of those things that are unpleasing to Him." - Apostolic Constitutions

Source:

See Apostolic Constitutions, Book 1.2," newadvent.org, CHURCH FATHERS: Apostolic Constitutions, Book I (newadvent.org).

"... forgetful of what believers had either done before in the times of the apostles, or always ought to do... In men, their beards were defaced; in women, their complexion was dyed; the eyes were falsified from what God's hand had made them; their hair was stained with a falsehood... They united in the bond of marriage with unbelievers; they prostituted the members of Christ to the Gentiles... And although it is written, You shall not mar the figure of your beard, Leviticus 19:27 he plucks out his beard, and dresses his hair..." - St. Cyprian of Carthage

Source:
St. Cyprian of Carthage, "Treatise 3," newadvent.org, CHURCH FATHERS: Treatise 3 (Cyprian of Carthage) (newadvent.org).

"But what is worse, and the opposite error, [is that] some cut off their beards, the mark of manhood, while often letting the hair of their heads grow long [like women]. And as to the beard, the sacred institution and teaching in the Ordinances of the Apostles says not to "spoil," that is, not to cut the beard, and not to deck oneself with meretricious ornaments or have the approach of pride as a copy of righteousness." - St. Epiphanios of Salamis [1]

"Just as one is forbidden to refrain from cutting his hair for the sake of beautification and good looks, and a bad purpose, so, on the other hand, it is also forbidden to cut it and to shave it with certain circularities roundabout, and, generally speaking, for the purpose of improving appearance and enhancing its attractiveness." - St. Epiphanios of Salamis [2]

Sources:

[1] The Panarion of Epiphanius of Salamis, Books II and III. De Fide, pg. 651: The Panarion of Epiphanius of Salamis, Books II and III. De Fide: Second ... - Google Books.

[2] J. Sanidopoulos, The Blessed Rasson, pg. 112.

(The following is a conversation between St. Iakavos of Evia and his spiritual child[ren]):

St. Iakavos: "“When we put on the cassock, we begin with the goal of sanctifying our soul. Care is necessary, however. For love of the world’s honor and glory, our egotism can make us lose our soul, rather than sanctify it... Priests shouldn’t cut their hair. In Asia Minor, when priests would comb their hair, they would put a white cloth down and whatever strands of hair fell, they would gather, put them in a little bag, and when they died, they would bury it with them. This is because, when the Holy Spirit descends during ordination, the priest is sanctified; even his hair is sanctified.”"

"A spiritual child of his that was listening to him at one time was thinking to himself: "Fine, they would gather the hairs; the nails, however, when they would cut them, what did they do with them, did they throw them away?"

Then the Elder, through his clairvoyant grace, recognized his thoughts, turned toward him, and said: "Their nails also they would gather.""

Sources:

See The Garden of the Holy Spirit: Elder Iakovos of Evia (1920-1991) as excerpted from “Saint Iakovos (Jacob, James) Tsalikis of Evia had great respect for priests and thought that priests were somehow angelic,” iconandlight.wordpress.com, Saint Iakovos (Jacob, James) Tsalikis of Evia had great respect for priests and thought that priests were somehow angelic. | iconandlight (wordpress.com). See also Ton Pateron Tis I. Monis Osiu David, Enas Agios Gerontas O Makaristos p. Iakavos (1993), pgs. 82-83 as cited in J. Sanidopoulos, The Blessed Rasson (1999), pg. 117.

"I am proud of the cassock I wear and consider it more valuable and seemly than every other kind of garment, even than the royal purple robes of kings. I consider myself unworthy to dress in such a modest, honorable and holy garb, which was honored by numberless monastic Saints, monk martyrs, confessors and Saints. I am saddened by and pity those clerics who reject the cassock and who shave their beards." - Blessed Elder Philotheos Zervakos of Paros

Source: H. Middleton, Precious Vessels of the Holy Spirit: The Lives and Counsels of Contemporary Elders of Greece (Protecting Veil Press: 2003). See also Concerning Priests and Holy Tradition: Excerpts from Precious Vessels of the Holy Spirit (orthodoxinfo.com)

"The priest's cassock is the flag of the Church of our Christ: for this reason we must try hard to honor it, we who wear it, with a holy life, so that those who don't wear it will honor and respect it." - St. Amphilochios of Patmos

Source: H. Middleton, Precious Vessels of the Holy Spirit: The Lives and Counsels of Contemporary Elders of Greece (Protecting Veil Press: 2003). See also Concerning Priests and Holy Tradition: Excerpts from Precious Vessels of the Holy Spirit (orthodoxinfo.com)

"The priest is the incarnation of the absolute, the expression of the constant, stable and unshakeable, the trumpet of Heaven, the image of incorruption, the mile-marker of eternity. May he remain forever unchanged, even in his external appearance, as a reminder and symbol of the ages and of the unchanging truths which he represents." - Blessed Elder Epiphanios of Athens

Source: H. Middleton, Precious Vessels of the Holy Spirit: The Lives and Counsels of Contemporary Elders of Greece (Protecting Veil Press: 2003). See also Concerning Priests and Holy Tradition: Excerpts from Precious Vessels of the Holy Spirit (orthodoxinfo.com)

(The following is a conversation between St. Paisios the Athonite and one of his spiritual children on proper clerical attire):

Question: 'Geronda, during the summer months when it’s so hot, is it still necessary for the Ecclesiasticos [sacristan] to serve in the church wearing the mantle? I find it so difficult.'

Answer: 'Oh, monastic life these days... What can I say? Saint Athanasios would wear a thick garment and a very heavy cross as part of his ascetic discipline, and look at us today! When I was in Australia, I even saw a sacristan in shorts. “This is perfect for the beach,” I told him. “It makes my job more comfortable wearing shorts,” he replied. People start thinking this way and end up saying, “Let’s get rid of our black cassocks, they're so hot in the sun.” Is the mantle in your way? Throw it away! Is your head-scarf a nuisance, because it makes you sweat? Throw it away! That is where we are heading. Now let’s get serious. If you get hot, wear lighter clothing underneath. We can all manage that.'

Question: 'Geronda, should someone [i.e. a monastic] take off the cassock and wear only the mantle? And the priests, should they remove their under-cassock [anteri] and wear only their pants?'

Answer: 'Well, what can I say? The mantle is the proper garment of the monk. During the tonsuring of a new monk, the mantle is worn by the sponsoring senior monk, who, after vesting the new monk with the cassock, removes his mantle and places it upon him. I was recently impressed by the fact that some women in Alexandria, Egypt, where it gets very hot would still keep their tradition and be dressed in black. And here we are, having such a hard time bearing the cassock, which has been bequeathed to us by our Fathers.'

Question: 'Geronda, there is this expression, “The cassock does not make one a priest.”'

Answer: 'Well, think of two olive trees, one with leaves and the other without. Which one do you prefer? Once, when I was at the Cell [Kalyvi] of the Holy Cross, I peeled the trunk of an olive tree and wrote this on it: “The trees got rid of their garments; it’s time to see the fruit of their labor!” Next to that I wrote, “A casssockless priest is a prodigal priest [Παπᾶς ἀράσωτος, ἄρα ἄσωτος].” At that time the cassock issue was being discussed in many circles, and some priests would come to me to get a blessing to remove them!'

Question: 'Geronda, someone brought an Orthodox priest wearing only trousers [without his cassock] to the monastery. Should we have asked for his blessing?'

Answer: 'What blessing? You should have told the person who brought him, no matter how important he was, “Forgive us, but it is a rule in our monastery to give cassocks to priests who are not wearing one. To have a priest come to an Orthodox women’s monastery wearing only his trousers! That is inappropriate.” When the person who brought him has no shame, and when the priest himself is not ashamed for having come without his cassock, why should you be embarrassed to ask him to put one on? I once met a young archimandrite wearing laymen’s clothing at an airport. He was going abroad and introduced himself, “I am Father so-and-so,” he said. “Where is your cassock?” was my answer. Of course, I did not bow to him [to receive his blessing].'

Question: 'Geronda, some people claim that a modernized clergy will be better able to help people.'

Answer: 'When Patriarch Demetrios visited the seminary of the Holy Cross in the United States, a few pious American students went up to him and said, “Your Holiness, don’t you think it’s time for clergy to be more up to date?” The Patriarchs response was, “Saint Cosmas said that when clergy turn into laymen, laymen will turn into demons.” Wasn’t that a good answer? Then they prepared this luxurious suite for him with a fancy bed and so on. The moment he saw it, he said, “Is this where I am supposed to stay, in this room? You’d better bring me a simple cot. When a clergyman becomes worldly, he becomes the devil’s candidate.””

Sources:
See Spiritual Counsels vol. I, pgs. 358-359. See online version here: Elder Paisios on Cassocks — Classical Christianity. See also “St Paisios: The clergy and the Church,” youtube.com, St Paisios : The clergy and the Church - YouTube. See also Hieromonk Isaac's Saint Paisios of Mount Athos, pgs. 199-200.

(The following are two more similar stories about St. Paisios the Athonite on the Cassock):

"Our final stories come from the life of the much-beloved holy elder Paisios (+1994) who lived a life of remarkable spiritual endeavor on the Holy Mountain. He would receive numerous visitors and was asked many questions which, no matter how difficult, he would always answer in a simple and straightforward manner, usually with some sort of an analogy. For instance, when a pilgrim came to him and inquired about the importance of a priest wearing a rasson [anteri/cassock], he answered that a priest without a rasson is like an orange without a peel. This he said to show that the rasson is a cover of protection which helps to preserve the flavor of the priesthood.

Another story told about Fr. Paisios is the following: ‘At one time some young monks who were well-groomed and modernistic came to visit Fr. Paisios and told him that there need[ed] to be changes in the outer appearance of the clergy and monks. The Elder, after the discussion, took them and brought them a large olive-tree, saying to them: “Here, here is a bishop,” and, showing them a smaller olive tree, he said to them “and here is a deacon.” He then took a sharp tool and horizontally chopped off its trunk.

After many months the monks again visited the Elder. He took them to show them the trees that had dried up, and told them: “This is how you will become if you change your attire.”

'A monk then told him: “Elder, didn't you feel sad for the olive trees?”

'“Here, my brother, the world is going to ruin and you think of the olive trees?” answered the Elder.'"

Source:

See John Sanidopoulos, The Blessed Rasson: A Plea For A Proper Orthodox Clerical Attire And Appearance In The Contemporary World (Charlotte, NC: Apologia: The Institute of Orthodox Christian Apologetic Research, 1999), 152-153.

(The following is about the holy Elder Joachim of St. Anne's Skete):

"His beard:

We must not omit saying a few words about Fr. Joachim's rare and exceptional beard.

When he lived in America, he observed with sorrow the modern spirit which had begun to affect even ecclesiastical matters. He saw priests who thought they could function better in society if they departed from Orthodox Tradition. In that worldly atmosphere, Fr. Joachim behaved courageously. He couldn't stand to see Orthodox priests taking off their precious riassas or cutting their hair and beard.

It is worth noting that before being tonsured, he made the following prayer to the Theotokos:

"Most Holy Theotokos, when I become a priest, please give me long hair and beard, so that I will look like the priests in my country."

The Mother of God did not deny him his supplication, but fulfilled his desire abundantly. As we stated earlier, the Americans wondered at his imposing appearance and his long, full beard. When he finally journeyed to Mount Athos, an astonishing thing happened. His beard grew and grew and lengthened all the way down his legs - a phenomenon very rare even in his fatherland. We attribute this to the prayer he made to the Mother of God. In order to move freely and restrain the remarks of others he was forced to carry his beard in a sack tied around his neck."

Source: Contemporary Ascetics of Mount Athos vol. 1, pgs. 83-84.

(The following is a conversation between St. Cosmas Aitolos and Orthodox laity):

St. Cosmas: "I ALSO SAY A WORD FOR MEN. It is natural for a man who is going on fifty years to wear a beard. But here I see old men who are sixty and eighty years old and still shave. Aren't you ashamed to shave? Doesn't God who gave us beards know better? Just as it is unseemly for an old woman to deck herself out and put on cosmetics, so it is for an old man to shave. When wheat grows and becomes white what does it signify?"

Orthodox Laymen: "Harvest."

St. Cosmas: "The same with man. When he grows up and [it] becomes white, what does this signify?"

Orthodox Laymen: "Death."

St. Cosmas: "Is there anyone here who wishes to let his beard grow? Let him stand up and tell me so we can become brothers, and I shall pray for him and ask all the Christians to forgive."

Orthodox Layman: "I, Teacher."

St. Cosmas: "Good, you have my blessing. Pray to God for me, a sinner, so that I will pray for you too for as long as I live. Will you do it?"

Orthodox Layman: "I will, O saint of God."

St. Cosmas: "I beg you, my fellow Christians, say three times for all those who let their beards grow: 'May God forgive and have mercy upon them.' Let Your nobility also ask for forgiveness. And may God enlighten you to let go of your sins as you let your beard grow - You, young men, honor those with beards. And if there is a man of thirty with a beard and one of fifty, or sixty, or a hundred who shaves, place the one with the beard above the one who shaves, in church as well as at the table. On the other hand, I don't say that a beard will get you to heaven, but good works will. And your dress should be modest, as well as your food and your drink. Your whole conduct should be Christian so that you will be a good example for others."

Source:

Father Kosmas Apostle of the Poor, pgs. 20-21. Online version here: Father-Kosmas-Apostle-of-the-Poor.pdf (stmaryofegypt.org).

(St. Nikodemos the Hagiorite's commentary on the 96th Canon of the 6th Ecumenical Council):

"Those too incur the excommunication of this Canon, according to Zonaras, who do not put a razor to their head at all, nor cut the hair of their head, but let it grow long enough to reach to the belt like that of women, and those who bleach their hair so as to make it blond or golden, or who twist it up and tie it on spills in order to make it curly; or who put wigs or “rats” on their head. This excommunication is incurred also by those who shave off their beard in order to make their face smooth and handsome after such treatment, and not to have it curly, or in order to appear at all times like beardless young men; and those who singe the hair of their beard with a red-hot tile so as to remove any that is longer than the rest, or more crooked; or who use tweezers to pluck out the superfluous hairs on their face, in order to become tender and appear handsome; or who dye their beard, in order not to appear to be old men. This same excommunication is incurred also by those women who use rouge and paint on their face, in order to look pretty, and in this way to attract men beholding them to their Satanic love. Oh, and how the miserable women have the hardihood to dishonor the image which God gave them with their wicked beautifications! Ah! how is God to recognize them and tell whether they are His own creatures and images, at a time when they are wearing another face which is devilish, and another image, which is that of Satan? Hence it is that St. Gregory the Theologian says the following in his epic verses:

“Build yourselves not towers of spurious tresses on your head, women,
While petting soft necks of rocks invisible;
Nor apply shameful paint to forms of God’s,
So as to be wearing masks, and not faces.
Lest God requite you for such things when He has come to resent them.
Who? Whence is the Creator? Avaunt, get thee away from me, strange female!
I did not paint thee a promiscuous woman, but created an image of myself.
How is it that I have an idol, a specter instead of a friend?”

And the poor wretches do not know that by what they are doing they are managing only to make themselves like that hag and whore called Jezebel (II Kings 9:30), and are themselves becoming new and second Jezebels, because she too used to paint her face in order to please the eyes of men, just as is written: “And when Jehu was come to Jezreel, Jezebel heard of him; and she painted her face, and attired her head, and peeped through the window” (ibid.). So all men and all women who do such things are all excommunicated by the present Ecumenical Council. And if these things are forbidden to be done by the laity in general, how much more they are forbidden to clerics and those in holy orders, who ought by their speech and by their conduct, and by the outward decency and plainness of their garments, and of their hair, and of their beard, to teach the laity not to be body-lovers and exquisites, but soul-lovers and virtue- lovers. Note that the present Canon censures the priests of the Latins who shave off their moustache and their beard and who look like very young men and handsome bridegrooms and have the face of women. For God forbids men of the laity in general to shave their beard, by saying: “Ye shall not mar the appearance of your bearded chin” (Lev. 19:27). But He especially forbids those in holy orders to shave their beard, by saying to Moses to tell the sons of Aaron, or, in other words, the priests, not to shave the skin of their bearded chin (Lev. 21:5). Not only did He forbid this in words, but He even appeared to Daniel with whiskers and beard as the Ancient of Days (Dan. 7:9); and the Son of God wore a beard while he was alive in the flesh. And our Forefathers and Patriarchs and Prophets and Apostles all wore beards, as is plainly evident from the most ancient pictures of them wherein they are painted with beards. But, more to the point, even the saints in Italy, like St. Ambrose, the father of monks Benedict, Gregory Dialogus, and the rest, all had beards, as they appear in their pictures painted in the church of St. Mark in Venice. Why, even the judgment of right reason decides the shaving of the beard to be improper. For the beard is the difference which in respect of appearance distinguishes a woman from a man. That is why a certain philosopher when asked why he grew a beard and whiskers, replied that as often as he stroked his beard and whiskers he felt that he was a man, and not a woman. Those men who shave their beard are not possessors of a manly face, but of a womanly face. Hence it was that Epiphanius blamed the Massalians for cutting off their beard, which is the visage peculiar to man as distinguished from woman. The Apostles in their Injunctions, Book I, ch.3, command that no one shall destroy the hair of his beard, and change the natural visage of the man into one that is unnatural. “For,” says he, “God the Creator made this to be becoming to women, but deemed it to be out of harmony with men.” The innovation of shaving the beard ensued in the Roman Church a little before Leo IX, Gregory VII even resorted to force in order to make bishops and clerics shave off their beard. Oh, and what a most ugly and most disgusting sight it is to see the successor of St. Peter close-shaven, as the Greeks say, like a “fine bridegroom,” with this difference, however, that he wears a stole and a pallium, and sits in the chief seat among a large number of other men like him in a council called the college of cardinals, while he himself is styled the Pope. Yet bearded Popes did not become extinct after insane Gregory, a witness to this fact being Pope Gelasius growing a beard, as is stated in his biography. See the Dodecabiblus of Dositheus, pp. 776-8. Meletius the Confessor (subject 7, concerning unleavened wafers) states that a certain Pope by the name of Peter on account of his lascivious acts was arrested by the king and one half of his beard was shaven off as ‘a mark of dishonor'. According to another authority, in other temples too there were princes, even on the sacerdotal list, who had a beard, as in Leipzig they are to be seen painted after Martin Luther in the church called St. Paul’s and that called St, Thomas’s. I saw the same things also in Bardislabia." - St. Nikodemos the Hagiorite

Source: The Rudder, pgs. 403-405.

For further reading see the following:
1. (A MUST READ! The most comprehensive, in-depth, well-researched resource on this topic!): John Sanidopoulos, The Blessed Rasson: A Plea For A Proper Orthodox Clerical Attire And Appearance In The Contemporary World (Charlotte, NC: Apologia: The Institute of Orthodox Christian Apologetic Research, 1999).

2. "Proper Clerical Dress and Attire," catalogueofstelisabethconvent.blogspot.com, Proper Clerical Dress and Attire - The Catalog of Good Deeds (catalogueofstelisabethconvent.blogspot.com).

3. "A Priest’s Cassock", orthodoxcityhermit.com, a priest’s cassock « ORTHODOX CHRISTIAN FAITH AND LIFE (orthodoxcityhermit.com).

4. Fr. Lawrence Farley, "Do Clerical Dress and Monastic Habits Really Matter?, obitel-minsk.com, Do Clerical Dress and Monastic Habits Really Matter? - The Catalog of Good Deeds (obitel-minsk.com).

5. "The Power of the Priestly Cassock," goodguyswearblack.org, The Power of the Priestly Cassock — Good Guys Wear Black | Discerning Your Vocation In The Orthodox Church.

6. "Concerning the Tradition of Long Hair and Beards," orthodoxinfo.com, Concerning the Tradition of Long Hair and Beards (orthodoxinfo.com).

7. Patrick Comerford, "Should priests shave? Should priests have beards?," patrickcomerford.com, Patrick Comerford: Should priests shave? Should priests have beards?