Midras 1 Tawarikh 1:4: Mekhilta DeRabbi Yishmael

And whence is it derived that the sons of Yonadav the son of Rechav are the descendants of Yithro? From (I Chronicles 2:55) "They were the Kenites, who descended from Chamath the father of Rechav." They sought a master and Yaavetz sought disciples, viz. (Ibid. 4:10) "and Yaavetz called out to the G–d of Israel, saying: 'If You bless me and expand my borders, and Your hand be with me and You keep (me) from evil, not to sadden me …' And the L–rd brought what he asked." "If you bless me" — with Torah study.. "and You expand my borders" — with disciples. "and Your hand be with me" — that I not forget my learning. "and You keep (me) from evil" — that You give me friends such as I am. "not to sadden me" — that the evil inclination not keep me from Torah study. "And the L–rd brought what he asked" — He granted him what he asked,

R. Yehudah Hanassi says: It is written "And Yaavetz called out to the G–d of Israel, saying: 'If You bless me and expand my borders, etc.'" If You bless me with children and expand my borders with sons and daughters, "and Your hand be with me" — in my dealings, "and You keep (me) from evil" — that the life You have given me be free of intestinal disorder, or eye ailments, or headaches, "not to sadden me" — that the evil inclination not sadden me … But if You do not do this for me, I will descend with my grief to the grave. "And the L–rd brought what he asked" — He granted him what he asked.