Numbers 3:6-9

6“Bring the tribe of Levi near and present them before Aaron the priest, so that they may serve him.

7They shall carry out the duties for him and for the whole congregation before the Tent of Meeting, doing the service of the tabernacle.

8They shall also take care of all the furnishings and utensils of the Tent of Meeting, and [attend to] the duties of the Israelites, doing the service of the tabernacle.

9You shall give the Levites to Aaron and to his sons [as servants and helpers]; they are to be given wholly to him from among the Israelites.