Leviticus 5:1-2

And if a soul sin, and hear the voice of swearing, and is a witness, whether he hath seen or known of it; if he do not utter it, then he shall bear his iniquity. Or if a soul touch any unclean thing, whether it be a carcase of an unclean beast, or a carcase of unclean cattle, or the carcase of unclean creeping things, and if it be hidden from him; he also shall be unclean, and guilty.