Matthew 7:16
14 How narrow is the gate and difficult the way that leads to life, and there are few who find it! 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.
Berakhot 48a
Babylonian TalmudThe Gemara relates that Abaye and Rava, when they were children, were seated before Rabba. Rabba said to them: To whom does one recite blessings? They said to him: To God, the All-Merciful. Rabba asked them: And where does the All-Merciful reside? Rava pointed to the ceiling. Abaye went outside and pointed toward the heaven. Rabba said to them: You will both become Sages. It is as the popular saying goes: A cucumber can be recognized from its blossoming stage. Similarly, a great person can be recognized even from a young age.
Notes and References
"... Something similar is true of sayings about fruit revealing character. These sayings generally express the commonsense idea that people reveal who they are through their behavior. Sirach says, 'Fruit discloses the tree; so a person’s speech discloses the cultivation of his mind.' That is, the fruit of a person's actions or words are the best way to learn who the person really is. A popular saying quoted in the Babylonian Talmud states that 'the young pumpkin is recognized by its sap,' which in context refers to wise comments of two boys indicating that they will become rabbis. (b. Berakhot 48a; See also Diogenianus, Paroemiae 5.15) The idea here is similar to Proverbs 20:11 ('Even children make themselves known by their acts'). None of these sayings suggest an unchanging human nature that manifests itself in predetermined ways. The point is something more commonsensical: it is possible to learn about people from what they do and say ..."
Eubank, Nathan "Good Trees Produce Good Fruit: Is Obedience Automatic According to the New Testament?" in Moffitt, David M. and Isaac Augustine Morales (eds.) A Scribe Trained for the Kingdom of Heaven: Essays on Christology and Ethics in Honor of Richard B. Hays (pp. 47-65) Fortress Academic, 2021