הלכה אויף מלכים א 2:3

Even as man is obliged to instruct his son, so is he obliged to teach his son's son, for it is said: "But make them known to thy sons and thy sons' sons" (Ibid. 4.9); and, not alone to his son and his son's son, but each and every scholar in Israel is commanded to instruct all who desire to be his disciples, even though they be not his sons, for it is said: "And thou shalt teach them diligently unto thy children" (Ibid. 6.7.), which is traditionally interpreted²Sifre, Deut. 11. C. G. to include one's disciples; for disciples, too, are called children, as it is said: "And the sons of the prophets came forth" (Second Kings, 2.3.). If it be so, why then was one commanded to teach his son and his son's son? To permit the precedence of one's son to one's son's son, and his son's son to the son of his fellow.³Sukkah, 30b; Kiddushin, 30. G.