Numbers 3:6-9

6“1Bring the tribe of Levi forward and present them before Aaron the priest, that they may serve him.

7They shall perform the duties for 2him and for the whole congregation in front of the tent of meeting, to do the 3service of the tabernacle.

8They shall also take care of all the furnishings of the tent of meeting, along with the duties of the sons of Israel, to do the service of the tabernacle.

9So you shall 4assign the Levites to Aaron and to his sons; they are exclusively assigned to him from the sons of Israel.