Numbers 8:5-7, 20-22

GOD spoke to Moses: “Take the Levites from the midst of the People of Israel and purify them for doing GOD’s work. This is the way you will do it: Sprinkle water of absolution on them; have them shave their entire bodies; have them scrub their clothes. Then they will have purified themselves.

Moses, Aaron, and the entire community of the People of Israel carried out these procedures with the Levites, just as GOD had commanded Moses. The Levites purified themselves and scrubbed their clothes. Then Aaron presented them as a Wave-Offering before GOD and made atonement for them to purify them. Only then did the Levites go to work at the Tent of Meeting. Aaron and his sons supervised them following the directions GOD had given.