Numbers 19:9; Numbers 19:17; Leviticus 8:6

And a man who is clean shall gather up tthe ashes of the heifer and deposit them outside the camp in a uclean place. And they shall be kept for the water for vimpurity for the congregation of the people of Israel; it is a sin offering.

17 For the unclean they shall take dsome ashes of the burnt sin offering, and fresh1 water shall be added in a vessel.

And Moses brought Aaron and his sons and washed them with water.