Numbers 8:5-8

5Then the Lord spoke to Moses:

6“Take the Levites from among the Israelites and purify them.

7And do this to them to purify them: Sprinkle water of purification on them; then have them shave all their body and wash their clothes, and so purify themselves.

8Then they are to take a young bull with its grain offering of fine flour mixed with olive oil; and you are to take a second young bull for a purification offering.