Tractate Pirkei Avot - Chapter 6 - Mishnah 3 אבות פרק ו׳ משנה ג׳

One who learns from his fellow one chapter, or one halakhah, or one verse, or one word, or even one letter, is obligated to treat him with honor; for so we find with David, king of Israel, who learned from Ahitophel no more than two things, yet called him his master, his guide and his beloved friend, as it is said, “But it was you, a man mine equal, my guide and my beloved friend” (Psalms 55:14). Is this not [an instance of the argument] “from the less to the greater” (kal vehomer)? If David, king of Israel who learned from Ahitophel no more than two things, nevertheless called him his master, his guide and his beloved friend; then in the case of one who learns from his fellow one chapter, or one halakhah, or one verse, or one word, or even one letter, all the more so he is under obligation to treat him with honor. And “honor’” means nothing but Torah, as it is said, “It is honor that sages inherit” (Proverbs 3:35). “And the perfect shall inherit good” (Proverbs 28:10), and “good” means nothing but Torah, as it is said, “For I give you good instruction; do not forsake my Torah” (Proverbs 4:2).