Numbers 19
18 Ref And a clean person is to take hyssop and put it in the water, shaking it over the tent, and all the vessels, and the people who were there, and over him by whom the bone, or the body of one who has been put to death with the sword, or the body of one who has come to his end by a natural death, or the resting-place was touched.
19 Ref Let the clean person do this to the unclean on the third day and on the seventh day: and on the seventh day he is to make him clean; and after washing his clothing and bathing himself in water, he will be clean in the evening.