Numbers 8:11-15

11And Aaron shall offer the Levites as a wave-offering before Jehovah from the children of Israel, and they shall perform the service of Jehovah.

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, to Jehovah, to make atonement for the Levites.

13And thou shalt set the Levites before Aaron, and before his sons, and offer them as a wave-offering to Jehovah.

14And thou shalt separate the Levites from among the children of Israel, that the Levites may be mine.

15And afterwards shall the Levites come in to do the service of the tent of meeting. And thou shalt cleanse them, and offer them as a wave-offering.