Leviticus 5:4-6

or if anyone thoughtlessly takes an oath to do anything, whether good or evil (in any matter one might carelessly swear about) even though they are unaware of it, but then they learn of it and realize their guilt— when anyone becomes aware that they are guilty in any of these matters, they must confess in what way they have sinned. As a penalty for the sin they have committed, they must bring to the LORD a female lamb or goat from the flock as a sin offering; and the priest shall make atonement for them for their sin.