Numbers 8:11-15

11Aaron is to present the Levites before the Lord as a wave offering from the Israelites, so that they may be ready to do the work of the Lord.

12“Then the Levites are to lay their hands on the heads of the bulls, using one for a sin offering to the Lord and the other for a burnt offering, to make atonement for the Levites.

13Have the Levites stand in front of Aaron and his sons and then present them as a wave offering to the Lord.

14In this way you are to set the Levites apart from the other Israelites, and the Levites will be mine.

15“After you have purified the Levites and presented them as a wave offering, they are to come to do their work at the tent of meeting.