Midrash su Ecclesiaste 11:1

Who were the Kenites? They were the descendants of Jethro, the father-in-law of Moses. It is said concerning them: Cast thy bread upon the waters, for thou shalt find it after many days (Eccles. 11:1). In reward for (his invitation to Moses): Call him that he may eat bread (Exod. 2:20). (This alludes to the bread. Regarding water) it is said concerning Moses (mosheh): Because I drew (meshah) him (out of the water (ibid., v. 10). Therefore the descendants of Jethro merited sitting in the chamber of hewn stone.⁸Thus Jethro cast his bread upon the waters of Moses’ Torah, and his descendants were suitably rewarded.