Beware of false prophets, which come to you in sheep's clothing, but inwardly they are ravening wolves. You shall know them by their fruits. Do men gather grapes of thorns, or figs of thistles? Even so every good tree brings forth good fruit; but a corrupt tree brings forth evil fruit. A good tree cannot bring forth evil fruit, neither can a corrupt tree bring forth good fruit. Every tree that brings not forth good fruit is hewn down, and cast into the fire. Wherefore by their fruits you shall know them. (Matthew 7:15-20)