Numbers 8:8-12

8Then they are to take a young bull with its grain offering of fine flour mixed with olive oil; and you are to take a second young bull for a purification offering.

9You are to bring the Levites before the tent of meeting and assemble the entire community of the Israelites.

10Then you are to bring the Levites before the Lord, and the Israelites are to lay their hands on the Levites;

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.