Numbers 19:7-8, 19

Then the priest shall wash his clothes and bathe his body in water, and afterward he may come into the camp. But the priest shall be unclean until evening. The one who burns the heifer shall wash his clothes in water and bathe his body in water and shall be unclean until evening.

And the clean person shall sprinkle it on the unclean on the third day and on the seventh day. Thus on the seventh day he shall cleanse him, and he shall wash his clothes and bathe himself in water, and at evening he shall be clean.