Numbers 3:5

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

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

5The LORD spoke to Moses, saying,

6“Bring the tribe of Levi near, and set them before Aaron the priest, that they may minister to him.

7They shall keep his requirements, and the requirements of the whole congregation before the Tent of Meeting, to do the service of the tabernacle.