Numbers 19:9-10

9And a man that is clean shall gather the ashes of the heifer, and lay them outside the camp in a clean place, and it shall be kept for the congregation of the children of Israel for a water of separation: it is a purification for sin. 10And he that gathereth the ashes of the heifer shall wash his clothes, and be unclean until the evening: and it shall be to the children of Israel, and to the stranger that sojourneth among them, for a statute for ever.