הלכה אויף מלכים ב 2:12

If one beholds his master transgressing the words of the Torah, he should say to him: "Our master, you have instructed us such and thus." Whenever he quotes a lecture in the presence of his master, he should say: "So have you, our master, instructed us." He must not repeat aught of his master's teachings unless he mentions the name of the one who said it. At the demise of his master, he should rend all of his garments until his chest be exposed, and he should never mend the garments. Whereat are these words directed? Only respecting his true master, of whom he learned most of his wisdom; but if he did not learn from him most of his wisdom, behold, he is no more to him than a fellow student and is not obliged to honor him in all the aforesaid matters. Nevertheless, he should rise before him, and at his demise, he should rend the garment even as he does rend at the demise of all whose loss he mourns. Even if one did not learn from his master but one word whether of great or of small importance, he should rise before him during his life-time and rend his garments at his demise.⁹Kiddushin, 32a; Berakot, 27b; Mo’ed Katan, 27a; Baba Mezi’a, 33a. C.