Numbers 8:20-22

Young's Literal Translation

²⁰ And Moses doth -- Aaron also, and all the company of the sons of Israel -- to the Levites according to all that Jehovah hath commanded Moses concerning the Levites; so have the sons of Israel done to them.

²¹ And the Levites cleanse themselves, and wash their garments, and Aaron waveth them a wave-offering before Jehovah, and Aaron maketh atonement for them to cleanse them,

²² and afterwards have the Levites gone in to do their service in the tent of meeting, before Aaron and before his sons; as Jehovah hath commanded Moses concerning the Levites, so they have done to them.