Numbers 8:7; Numbers 8:21

7 "Thus you shall do to them, for their cleansing: sprinkle purifying water on them, and let them use a razor over their whole body and wash their clothes, and they will be clean.

21 The Levites, too, purified themselves from sin and washed their clothes; and Aaron presented them as a wave offering before the LORD . Aaron also made atonement for them to cleanse them.