Second Council of Nicaea, Canon XXII

That when it happens that monks have to eat with women they ought to observe giving of thanks, and abstemiousness, and discretion.

To surrender all things to God, and not to serve our own wills, is great gain.  For says the divine Apostle, “whether ye eat or drink, do all to the glory of God.”  And Christ our God has bidden us in his Gospels, to cut off the beginning of sins; for not only is adultery rebuked by him, but even the movement of the mind towards the act of adultery when he says, “Whosoever looketh on a woman to lust after her, hath committed adultery with her already in his heart.”  We who have been thus taught ought therefore to purify our minds.  Now although all things are lawful, all things are not expedient, as we have been taught by the mouth of the Apostle.  It is needful that all men should eat in order that they may live.  And for those to whom life consists of marrying, and bringing forth children, and of the condition of the lay state, there is nothing unbecoming in men and women eating together, only let them give thanks to the giver of the food; but if there be the entertainments of the theatre, that is, Satanic songs accompanied with the meretricious inflections of harps, there come upon them, through these things, the curse of the prophet, who thus speaks:  “Woe to them who drink wine with harp and psaltery, but they regard not the works of the Lord, and consider not the works of his hands.”  Whenever persons of this sort are found among Christians, let them amend their ways; but if they will not do so, let there overtake them the penalties which have been enacted in the canons by our predecessors.  With regard to those whose life is free from care and apart from men, that is, those who have resolved before the Lord God to carry the solitary yoke, they should sit down alone and in silence.  Moreover it is also altogether unlawful for those who have chosen the priestly life to eat in private with women, unless it be with God-fearing and discreet men and women, so that even their feast may be turned to spiritual edification.  The same rule is to be observed with relatives.  Again, if it happen that a monk or priest while on a journey does not have with him what is absolutely necessary for him, and, because of his pressing needs, thinks well to turn aside into an inn or into someone’s house, this he is permitted to do, seeing that need compels.

Translation: Henry R. Percival, The Seven Ecumenical Councils, NPNF II.14 (1900), via CCEL.