Numbers 8:8-12

8Then let them take a bull from the herd and its grain offering of fine flour mixed with oil, and you shall take another bull from the herd for a sin offering.

9And you shall bring the Levites before the tent of meeting and assemble the whole congregation of the people of Israel.

10When you bring the Levites before the Lord, the people of Israel shall lay their hands on the Levites,

11and Aaron shall offer the Levites before the Lord as a wave offering from the people of Israel, that they may do the service of the Lord.

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