Numbers Chapter 8

8:6-11
Take the Levites from among the children of Israel, and cleanse them.
And thus shall 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 thou shalt bring the Levites before the Lord: and the children of Israel shall put their hands upon the Levites:
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.