Numbers 8:9

7And 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.

8Then 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.

9And thou shalt bring the Levites before the tabernacle of the congregation: and thou shalt gather the whole assembly of the children of Israel together:

10And thou shalt bring the Levites before the LORD: and the children of Israel shall put their hands upon the Levites:

11And 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.