Sirach 27:6
Ben Sira, Ecclesiasticus3 If a person is not steadfast in the fear of the Lord, his house will be quickly overthrown. 4 When a sieve is shaken, the refuse appears; so do a person's faults when he speaks. 5 The kiln tests the potter's vessels; so the test of a person is in his conversation. 6 Its fruit discloses the cultivation of a tree; so a person's speech discloses the cultivation of his mind. 7 Do not praise anyone before he speaks, for this is the way people are tested.
Matthew 7:19
15 “Watch out for false prophets, who come to you in sheep’s clothing but inwardly are voracious wolves. 16 You will recognize them by their fruit. Grapes are not gathered from thorns or figs from thistles, are they? 17 In the same way, every good tree bears good fruit, but the bad tree bears bad fruit. 18 A good tree is not able to bear bad fruit, nor a bad tree to bear good fruit. 19 Every tree that does not bear good fruit is cut down and thrown into the fire. 20 So then, you will recognize them by their fruit.
Notes and References
"... In Judaism the Old Testament already distinguished between true and false prophets, and one can see that the notion of 'pseudo-prophet' becomes more conspicuous in the LXX, in Josephus, and in Philo. Primitive Christianity from early on developed its own version of false prophecy, so that by the time of the SM the existence of Christian false prophets could be taken for granted. They not only existed, but they posed a serious threat to the community, so much so that a special warning against them was felt to be in order. The section as a whole has two concerns. First, there is the traditional warning against such false prophets; second, given the danger these people present, a method for their detection is recommended. This method takes its clues from agricultural experience and wisdom. It sounds somewhat simplistic, but in reality it is not. (See also Sirach 27:6 ... also Jeremiah 17:10) The experiences referred to in verses 16b and 17-19 are merely examples of a more general truth, so that the simplicity is deceptive. Heinrici clearly recognized this point, and referred to parallels in Aristotle ..."
Betz, Hans Dieter, and Adela Yarbro Collins The Sermon on the Mount: A Commentary on the Sermon on the Mount, Including the Sermon on the Plain (p. 529) Fortress Press, 1995