Numbers 3:4-6

King James Version

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.