Numbers 8:7

8:7 And do this to them to purify them: Sprinkle water of purification on them; then have them shave all their body and wash their clothes, and so purify themselves.

Numbers 19:9

19:9 “‘Then a man who is ceremonially clean must gather up the ashes of the red heifer and put them in a ceremonially clean place outside the camp. They must be kept for the community of the Israelites for use in the water of purification – it is a purification for sin.

Numbers 19:17

19:17 “‘For a ceremonially unclean person you must take some of the ashes of the heifer burnt for purification from sin and pour fresh running water over them in a vessel.