Leviticus 5:1, 6

“If anyone sins in that he hears a public adjuration to testify, and though he is a witness, whether he has seen or come to know the matter, yet does not speak, he shall bear his iniquity

he shall bring to the LORD as his compensation for the sin that he has committed, a female from the flock, a lamb or a goat, for a sin offering. And the priest shall make atonement for him for his sin.