Nicene and Post-Nicene Fathers, Vol. III:
Moral Treatises of St. Augustin: Section 33

33. And, the case being thus, enough and more than enough answer has been made to the heretics, whether they be Manichees, or whosoever other that bring false charges against the Fathers of the Old Testament, on the subject of their having several wives, thinking this a proof whereby to convict them of incontinence: provided, that is, that they perceive, that that is no sin, which is committed neither against nature, in that they used those women not for wantonness, but for the begetting of children: nor against custom, forasmuch as such things were usually done at those times: nor against command, forasmuch as they were forbidden by no law. But such as used women unlawfully, either the divine sentence in those Scriptures convicts them, or the reading sets them forth for us to condemn and shun, not to approve or imitate.