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.
(non occ.) But from their actions we may conjecture whether this their outward appearance is put on for display. For when by any temptations those things are withdrawn or denied them which they had either attained or sought to attain by this evil, then needs must that it appear whether they be the wolf in sheep’s clothing, or the sheep in his own.