Numbers 8:11

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

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

And 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 the LORD, to make an atonement for the Levites.

And thou shalt set the Levites before Aaron, and before his sons, and offer them for an offering unto the LORD.