Numbers 19:9-10

9“A man who is clean is to gather up the cow’s ashes and deposit them outside the camp in a ceremonially clean place. The ashes will be kept by the Israelite community for preparing the water to remove impurity; it is a sin offering.

10Then the one who gathers up the cow’s ashes must wash his clothes, and he will remain unclean until evening. This is a permanent statute for the Israelites and for the alien who resides among them.