Leviticus 5:2-6

Or if a person touches any unclean thing, whether a carcass of an unclean beast or the carcass of unclean cattle or a carcass of unclean swarming things, though it is hidden from him and he is unclean, then he will be guilty. Or if he touches human uncleanness, of whatever sort his uncleanness may be with which he becomes unclean, and it is hidden from him, and then he comes to know it, he will be guilty. Or if a person swears thoughtlessly with his lips to do evil or to do good, in whatever matter a man may speak thoughtlessly with an oath, and it is hidden from him, and then he comes to know it, he will be guilty in one of these. So it shall be when he becomes guilty in one of these, that he shall confess that in which he has sinned. He shall also bring his guilt offering to the LORD for his sin which he has committed, a female from the flock, a lamb or a goat as a sin offering. So the priest shall make atonement on his behalf for his sin.