Numbers 19:9-10

9And a man that is clean shall gather up the ashes of the heifer, and lay them up without the camp in a clean place; and it shall be kept for the congregation of the children of Israel for a water for impurity: it is a sin-offering. 10And he that gathereth the ashes of the heifer shall wash his clothes, and be unclean until the even: and it shall be unto the children of Israel, and unto the stranger that sojourneth among them, for a statute for ever.