Numbers 3:4-9

Nadab and Abihu, however, died before the LORD when they made an offering with unauthorized fire before him in the Desert of Sinai. They had no sons, so Eleazar and Ithamar served as priests during the lifetime of their father Aaron. The LORD said to Moses, “Bring the tribe of Levi and present them to Aaron the priest to assist him. They are to perform duties for him and for the whole community at the tent of meeting by doing the work of the tabernacle. They are to take care of all the furnishings of the tent of meeting, fulfilling the obligations of the Israelites by doing the work of the tabernacle. Give the Levites to Aaron and his sons; they are the Israelites who are to be given wholly to him.