John Cassian, The Institutes VIII.15: How the Old Law would root out anger not only from the actions but from the thoughts

But why should we spend any more time over evangelic and apostolic precepts, when even the old law, which is thought to be somewhat slack, guards against the same thing, when it says, “Thou shalt not hate thy brother in thine heart;” and again, “Be not mindful of the injury of thy citizens;” and again, “The ways of those who preserve the recollection of wrongs are towards death”? You see there too that wickedness is restrained not only in action, but also in the secret thoughts, since it is commanded that hatred be utterly rooted out from the heart, and not merely retaliation for, but the very recollection of, a wrong done.