Numbers 8:20-22

Amplified Bible

²⁰ Thus Moses and Aaron and all the congregation of the children of Israel did [these things] to the Levites; in accordance with all that the Lord had commanded Moses concerning the Levites, so the Israelites did to them. ²¹ The Levites, too, purified themselves from sin and they washed their clothes; and Aaron presented them as a wave offering before the Lord, and Aaron made atonement for them to cleanse them. ²² Then after that the Levites went in to perform their service in the Tent of Meeting before Aaron and his sons; just as the Lord had commanded Moses concerning the Levites, so they did to them.