Numbers 8:10 (KJV)

And the LORD spake unto Moses, saying,

Take the Levites from among the children of Israel, and cleanse them.

And thus shalt thou do unto them, to cleanse them: Sprinkle water of purifying upon them, and let them shave all their flesh, and let them wash their clothes, and so make themselves clean.

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

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 Aaron shall offer the Levites before the LORD for an offering of the children of Israel, that they may execute the service of the LORD.

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.

Thus shalt thou separate the Levites from among the children of Israel: and the Levites shall be mine.

And after that shall the Levites go in to do the service of the tabernacle of the congregation: and thou shalt cleanse them, and offer them for an offering.