Numbers 3:6

3 These are the names of the sons of Aaron, the priests which were anointed, whom he consecrated to minister in the priest's office.

4 And Nadab and Abihu died before the LORD, when they offered strange fire before the LORD, in the wilderness of Sinai, and they had no children: and Eleazar and Ithamar ministered in the priest's office in the sight of Aaron their father.

5 And the LORD spake unto Moses, saying,

6 Bring the tribe of Levi near, and present them before Aaron the priest, that they may minister unto him.

7 And they shall keep his charge, and the charge of the whole congregation before the tabernacle of the congregation, to do the service of the tabernacle.

8 And they shall keep all the instruments of the tabernacle of the congregation, and the charge of the children of Israel, to do the service of the tabernacle.

9 And thou shalt give the Levites unto Aaron and to his sons: they are wholly given unto him out of the children of Israel.