Numbers 8:20-22

American Standard Version

²⁰ Thus did Moses, and Aaron, and all the congregation of the children of Israel, unto the Levites: according unto all that Jehovah commanded Moses touching the Levites, so did the children of Israel unto them. ²¹ And the Levites purified themselves from sin, and they washed their clothes: and Aaron offered them for a wave-offering before Jehovah; and Aaron made atonement for them to cleanse them. ²² And after that went the Levites in to do their service in the tent of meeting before Aaron, and before his sons: as Jehovah had commanded Moses concerning the Levites, so did they unto them.