Babylonian Talmud, Ta'anit 7a -1

Rav Nahman bar Isaac said: Why are the words of the Torah compared to a tree, as it is said: “She is a tree of life to them that lay hold upon her” (Proverbs 3:18)? This is to tell you that, as a small log may set fire to a large log, so do the lesser scholars sharpen the wits of the greater. And Rabbi Hanina said the same: Much have I learned from my masters, and more from any colleagues than from my masters, and from my disciples the most. [Translation by CAJE]