Numbers 8:11-15

11and 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.

12When 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.

13You are to have the Levites stand before Aaron and his sons, and then offer them as a wave offering to the Lord.

14And so you are to separate the Levites from among the Israelites, and the Levites will be mine.

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.