Numbers 19:9, 18

“Then someone who is clean will collect the ashes from the cow and put them in a clean place outside the camp. The Israelites will keep these ashes to use in the cleansing water, in a special ceremony to cleanse away sin.

A clean person must take a hyssop branch and dip it into the water, and then he must sprinkle it over the tent and all its objects. He must also sprinkle the people who were there, as well as anyone who touched a bone, or the body of someone who was killed, or a dead person, or a grave.