Leviticus 5:4-10

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.

7If, however, he cannot afford a lamb, he may bring to the LORD as restitution for his sin two turtledoves or two young pigeons—one as a sin offering and the other as a burnt offering. 8He is to bring them to the priest, who shall first present the one for the sin offering. He is to twist its head at the front of its neck without severing it; 9then he is to sprinkle some of the blood of the sin offering on the side of the altar, while the rest of the blood is drained out at the base of the altar. It is a sin offering. 10And the priest must prepare the second bird as a burnt offering according to the ordinance. In this way the priest will make atonement for him for the sin he has committed, and he will be forgiven.