Numbers 19:9-10

9“A man who is clean  will collect the ashes from the cow and put them in a clean place outside the camp. They will be kept by the community of Israel and used in the water that takes away uncleanness. The cow is an offering for sin.

10The person who collected the ashes from the cow must also wash his clothes. He will be unclean until evening. This will be a permanent law for the Israelites and for the foreigners who live with them.