Numbers 1:50

1:50 But appoint the Levites over the tabernacle of the testimony, over all its furnishings and over everything in it. They must carry the tabernacle and all its furnishings; and they must attend to it and camp around it.

Numbers 8:11

8:11 and Aaron is to offer the Levites before the Lord as a wave offering from the Israelites, that they may do the work of the Lord.

Numbers 8:15

8:15 “After this, the Levites will go in to do the work of the tent of meeting. So you must cleanse them and offer them like a wave offering.

Numbers 8:24-26

8:24 “This is what pertains to the Levites: At the age of twenty-five years and upward one may begin to join the company in the work of the tent of meeting, 8:25 and at the age of fifty years they must retire from performing the work and may no longer work. 8:26 They may assist their colleagues in the tent of meeting, to attend to needs, but they must do no work. This is the way you must establish the Levites regarding their duties.”