Leviticus 5:1-2

‘If anyone sins after he hears a public adjuration (solemn command to testify) when he is a witness, whether he has seen or [otherwise] known [something]—if he fails to report it, then he will bear his guilt and be held responsible. Or if someone touches any [ceremonially] unclean thing—whether the carcass of an unclean wild animal or the carcass of an unclean domestic animal or the carcass of unclean creeping things—even if he is unaware of it, he has become unclean, and he will be guilty.