Numbers 8:19-21

American Standard Version

¹⁹ And I have given the Levites as ^[a]a gift to Aaron and to his sons from among the children of Israel, to do 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, ^[b]when the children of Israel come nigh unto the sanctuary.

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.