Numbers 8:20

8:20 So Moses and Aaron and the entire community of the Israelites did this with the Levites. According to all that the Lord commanded Moses concerning the Levites, this is what the Israelites did with them.

Numbers 8:24

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,

Numbers 8:26

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.”