In like manner also the younger men must be blameless in all things, caring for purity before everything and curbing themselves from every evil. For it is a good thing to refrain from lusts in the world, for every lust wars against the Spirit, and neither whoremongers nor effeminate persons nor defilers of themselves with men shall inherit the kingdom of God, neither they that do untoward things. Wherefore it is right to abstain from all these things, submitting yourselves to the presbyters and deacons as to God and Christ. The virgins must walk in a blameless and pure conscience.
Shepherd of Hermas
“I charge you,” said he, “to keep purity, and let not a thought enter into your heart concerning another’s wife, or concerning fornication, or concerning any such like evil deeds; for in so doing you commit a great sin. But remember your own wife always, and you shall never go wrong.”
“Not only,” said he, “is it adultery, if a man pollute his flesh, but whosoever does things like unto the heathen commits adultery. If therefore in such deeds as these likewise a man continue and repent not, keep away from him, and live not with him. Otherwise, you also are a partaker of his sin.” – ibid
“If a wife, Sir,” say I, “or, it may be, a husband fall asleep, and one of them marry, does the one that marries sin?” “He sins not,” said he, “but if he remain single, he invests himself with more exceeding honor and with great glory before the Lord; yet even if he should marry, he sins not. Preserve purity and holiness therefore, and you shall live unto God.” – ibid
But we are so far from practicing promiscuous intercourse, that it is not lawful among us to indulge even a lustful look. “For,” said He, “he that looks on a woman to lust after her, has committed adultery already in his heart.” Those, then, who are forbidden to look at anything more than that for which God formed the eyes, which were intended to be a light to us, and to whom a wanton look is adultery, the eyes being made for other purposes, and who are to be called to account for their very thoughts, how can any one doubt that such persons practice self-control?
And their (Christian) women, O King, are pure as virgins, and their daughters are modest; and their men keep themselves from every unlawful union and from all uncleanness, in the hope of a recompense to come in the other world.
Clement of Alexandria
Wherefore also the Lord commands “to watch,” so that our soul may never be perturbed with passion, even in dreams; but also to keep the life of the night pure and stainless, as if spent in the day. For assimilation to God, as far as we can, is preserving the mind in its relation to the same things. And this is the relation of mind as mind.