Leviticus 5:4-6

4Or if someone swears thoughtlessly with his lips to do anything good or evil—in whatever matter a man may rashly pronounce an oath—even if he is unaware of it, when he realizes it, he is guilty in the matter.

5If someone incurs guilt in one of these ways, he must confess the sin he has committed, 6and he must bring his guilt offering to the LORD for the sin he has committed: a female lamb or goat from the flock as a sin offering. And the priest will make atonement for him concerning his sin.