Numbers 19:9-10

9And a clean man shall gather the ashes of the heifer, and deposit them outside the camp in a clean place, and it shall be kept for the assembly of the children of Israel for a water of separation: it is a purification for sin.

10And he that hath gathered 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, an everlasting statute.