Numbers 3:4-6

American Standard Version

⁴ 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.

⁵ And Jehovah spake unto Moses, saying, ⁶ Bring the tribe of Levi near, and set them before Aaron the priest, that they may minister unto him.