Numbers 3:4-9

And Nadab and Abihu died before Jehovah, when they offered strange fire before Jehovah, in the wilderness of Sinai, and they had no children; and Eleazar and Ithamar ministered in the priest’s office in the presence of Aaron their father. And Jehovah spake unto Moses, saying, Bring the tribe of Levi near, and set them before Aaron the priest, that they may minister unto him. And they shall keep his charge, and the charge of the whole congregation before the tent of meeting, to do the service of the tabernacle. And they shall keep all the furniture of the tent of meeting, and the charge of the children of Israel, to do the service of the tabernacle. And thou shalt give the Levites unto Aaron and to his sons: they are wholly given unto him on the behalf of the children of Israel.