Numbers 19:7-8, 19

After the priest has washed himself and his clothes with water, he may come back into the camp, but he will be unclean until evening. The man who burns the cow must wash himself and his clothes in water; he will be unclean until evening.

The person who is clean must sprinkle this water on the unclean people on the third day and on the seventh day. On the seventh day they will become clean. They must wash their clothes and take a bath, and they will be clean that evening.