Numbers 19:16
And whosoever toucheth one that is slain with a sword in the open fields, or a dead body, or a bone of a man, or a grave, shall be unclean seven days. And whosoever toucheth one that is slain with a sword in the open fields, or a dead body, or a bone of a man, or a grave, shall be unclean seven days.
Anyone who touched a person killed by a sword out in the open field became ritually unclean for seven days. The same seven-day uncleanness came by touching a dead body, a human bone, or a grave. Kept in the home, an unholy person brings uncleanness into it in the same figurative sense. To harbor such a person is therefore to defile the household as surely as contact with death defiled under that rule.