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 9:6-7

9:6 It happened that some men who were ceremonially defiled by the dead body of a man could not keep the Passover on that day, so they came before Moses and before Aaron on that day. 9:7 And those men said to him, “We are ceremonially defiled by the dead body of a man; why are we kept back from offering the Lord’s offering at its appointed time among the Israelites?”

Numbers 9:10

9:10 “Tell the Israelites, ‘If any of you or of your posterity become ceremonially defiled by touching a dead body, or are on a journey far away, then he may observe the Passover to the Lord.