Numbers 19:9-10

9And a man who is clean shall gather up the ashes of the heifer and deposit them outside the camp in a clean place. And they shall be kept for the water for impurity for the congregation of the people of Israel; it is a sin offering.

10And the one who gathers the ashes of the heifer shall wash his clothes and be unclean until evening. And this shall be a perpetual statute for the people of Israel, and for the stranger who sojourns among them.