Numbers 19:10-12

10The one who gathers the ashes of the heifer shall wash his clothes, and be unclean until evening. This shall be a perpetual statute to the Israelites and to the stranger who lives as a resident alien among them.

11‘The one who touches the dead body of any person shall be unclean for seven days.

12That one shall purify himself from uncleanness with the water [made with the ashes of the burned heifer] on the third day and on the seventh day, and then he will be clean; but if he does not purify himself on the third day and on the seventh day, he will not be clean.