Nicene and Post-Nicene Fathers, Vol. V:
On Marriage and Concupiscence.: Chapter 17

Chapter 17 [XV.]—What is Sinless in the Use of Matrimony? What is Attended With Venial Sin, and What with Mortal?

It is, however, one thing for married persons to have intercourse only for the wish to beget children, which is not sinful: it is another thing for them to desire carnal pleasure in cohabitation, but with the spouse only, which involves venial sin. For although propagation of offspring is not the motive of the intercourse, there p. 271 is still no attempt to prevent such propagation, either by wrong desire or evil appliance. They who resort to these, although called by the name of spouses, are really not such; they retain no vestige of true matrimony, but pretend the honourable designation as a cloak for criminal conduct. Having also proceeded so far, they are betrayed into exposing their children, which are born against their will. They hate to nourish and retain those whom they were afraid they would beget. This infliction of cruelty on their offspring so reluctantly begotten, unmasks the sin which they had practised in darkness, and drags it clearly into the light of day. The open cruelty reproves the concealed sin. Sometimes, indeed, this lustful cruelty, or, if you please, cruel lust, resorts to such extravagant methods as to use poisonous drugs to secure barrenness; or else, if unsuccessful in this, to destroy the conceived seed by some means previous to birth, preferring that its offspring should rather perish than receive vitality; or if it was advancing to life within the womb, should be slain before it was born. Well, if both parties alike are so flagitious, they are not husband and wife; and if such were their character from the beginning, they have not come together by wedlock but by debauchery. But if the two are not alike in such sin, I boldly declare either that the woman is, so to say, the husband’s harlot; or the man the wife’s adulterer.