Leviticus 5:1, 6

‘If a person sins in hearing the utterance of an oath, and is a witness, whether he has seen or known of the matter—if he does not tell it, he bears guilt.

and he shall bring his trespass offering to the LORD for his sin which he has committed, a female from the flock, a lamb or a kid of the goats as a sin offering. So the priest shall make atonement for him concerning his sin.