NUMERI 8:21

E i Leviti si purificarono, e lavarono i lor vestimenti. E Aaronne li presentò per offerta davanti al Signore, e fece purgamento per loro, per purificarli.

And the Levites were purified, and they washed their clothes; and Aaron offered them as an offering before the LORD; and Aaron made an atonement for them to cleanse them.