Leviticus 5:4-6

4Or if someone swears rashly to do what is good or evil — concerning anything a person may speak rashly in an oath — without being aware of it, but later recognizes it, he incurs guilt in such an instance.

5If someone incurs guilt in one of these cases, he is to confess he has committed that sin.

6He must bring his penalty for guilt for the sin he has committed to the Lord: a female lamb or goat from the flock as a sin offering. In this way the priest will make atonement on his behalf for his sin.