Numbers 19:16, 18

If anyone is outside and touches someone who was killed by a sword or who died a natural death, or if anyone touches a human bone or a grave, that person will be unclean for seven days.

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.