Numbers 8:8-12

8Then let them take a young bullock with his grain offering, even fine flour mingled with oil, and another young bullock shalt thou take for a sin offering.

9And thou shalt bring the Levites before the tabernacle of the congregation: and thou shalt gather the whole assembly of the children of Israel together:

10And thou shalt bring the Levites before Yhwh: and the children of Israel shall put their hands upon the Levites:

11And Aaron shall offer the Levites before Yhwh for an offering of the children of Israel, that they may execute the service of Yhwh.123

12And the Levites shall lay their hands upon the heads of the bullocks: and thou shalt offer the one for a sin offering, and the other for a burnt offering, unto Yhwh, to make an atonement for the Levites.