Numbers 8:20-21

New King James Version

²⁰ Thus Moses and Aaron and all the congregation of the children of Israel did to the Levites; according to all that the Lord commanded Moses concerning the Levites, so the children of Israel did to them. ^21 (A)And the Levites purified themselves and washed their clothes; then Aaron presented them like a wave offering before the Lord, and Aaron made atonement for them to cleanse them.