Numbers 19:12, 19

He shall cleanse himself with the water on the third day and on the seventh day, and so be clean. But if he does not cleanse himself on the third day and on the seventh day, he will not become clean.

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.