Numbers 3:4-6

Darby Translation

⁴ And Nadab and Abihu died before Jehovah when they offered strange fire before Jehovah in the wilderness of Sinai, and they had no sons; and Eleazar and Ithamar exercised the priesthood in the presence of Aaron their father.

⁵ And Jehovah spoke to Moses, saying,

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