Be on the watch for false prophets, who come to you in sheep’s clothing, but inside they are cruel wolves. By their fruits you will get knowledge of them. Do men get grapes from thorns or figs from thistles? Even so, every good tree gives good fruit; but the bad tree gives evil fruit. It is not possible for a good tree to give bad fruit, and a bad tree will not give good fruit. Every tree which does not give good fruit is cut down and put in the fire. So by their fruits you will get knowledge of them. (Matthew, 7:15-20)