Numbers 8:11-13

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. 8:12 When the Levites lay their hands on the heads of the bulls, offer the one for a purification offering and the other for a whole burnt offering to the Lord, to make atonement for the Levites. 8:13 You are to have the Levites stand before Aaron and his sons, and then offer them as a wave offering to 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.