Numbers 3:4-6

New Century Version

⁴ But Nadab and Abihu died in the presence of the Lord when they offered the wrong kind of fire before the Lord in the Desert of Sinai. They had no sons. So Eleazar and Ithamar served as priests during the lifetime of their father Aaron.

⁵ The Lord said to Moses, ⁶ “Bring the tribe of Levi and present them to Aaron the priest to help him.