Numbers 19:9-10

9Then a man who is ceremonially clean is to gather up the ashes of the heifer and store them in a ceremonially clean place outside the camp. They must be kept by the congregation of Israel for preparing the water of purification; this is for purification from sin. 10The man who has gathered up the ashes of the heifer must also wash his clothes, and he will be ceremonially unclean until evening. This is a permanent statute for the Israelites and for the foreigner residing among them.