Numbers 8:12-14

“Next the Levites will lay their hands on the heads of the young bulls. Present one as a sin offering and the other as a burnt offering to the LORD, to purify the Levites and make them right with the LORD. Then have the Levites stand in front of Aaron and his sons, and raise your hands and present them as a special offering to the LORD. In this way, you will set the Levites apart from the rest of the people of Israel, and the Levites will belong to me.