You are to gird Aaron and his sons with sashes, tie headwear on them, and they shall hold the priesthood by a perpetual statute. In this way you are to consecrate Aaron and his sons.
Moses spoke to Aaron and to Eleazar and Itamar his surviving sons: “Take the grain offering left over from Adonai’s offerings by fire, and eat it without hametz beside the altar, for it is most holy.
But you and your sons with you are to maintain your priesthood for everything pertaining to the altar and inside the parokhet . I am giving you the ministry of the priesthood as a gift. Anyone unauthorized who approaches will die.”
But Nadab and Abihu died before Adonai for offering unauthorized fire before Adonai in the Sinai wilderness—they had no children. So Eleazar and Ithamar served as kohanim under Aaron their father.