Numbers 8:19-21

Darby Translation

¹⁹ And I have given the Levites as a gift to Aaron and to his sons, from among the children of Israel, to perform the service of the children of Israel in the tent of meeting, and to make atonement for the children of Israel; that there be no plague among the children of Israel, when the children of Israel draw near to the sanctuary.

²⁰ And Moses and Aaron, and all the assembly of the children of Israel, did to the Levites according to all that Jehovah had commanded Moses concerning the Levites: so did the children of Israel to them.

²¹ And the Levites purified themselves from sin, and they washed their garments; and Aaron offered them as a wave-offering before Jehovah; and Aaron made atonement for them to cleanse them.