Augustine of Hippo
Catena Aurea · Matthäusevangelium 7
Beware of false prophets, which come to you in sheep’s clothing, but inwardly they are ravening wolves. Ye shall know them by their fruits. Do men gather grapes of thorns, or figs of thistles? Even so every good tree bringeth forth good fruit; but a corrupt tree bringeth forth evil fruit. A good tree cannot bring forth evil fruit, neither can a corrupt tree bring forth good fruit. Every tree that bringeth not forth good fruit is hewn down, and cast into the fire. Wherefore by their fruits ye shall know them.
(vid. Op. Imp. in. Jul. v. 40. &c. et alibi.) But as it is manifest that all evil works proceed from an evil will, as its fruits from an evil tree; so of this evil will itself whence will you say that it has sprung, except that the evil will of an angel sprung from an angel, of man from man? And what were these two before those evils arose in them, but the good work of God, a good and praiseworthy nature. See then out of good arises evil; nor was there any thing at all out of which it might arise but what was good. I mean the evil will itself, since there was no evil before it, no evil works, which could not come but from evil will as fruit from an evil tree. Nor can it be said that it sprung out of good in this way, because it was made good by a good God; for it was made of nothing, and not of God.