Leviticus 5:8

5 If someone incurs guilt in one of these ways, he must confess the sin he has committed,

6 and 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.

7 If, 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.

8 He 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;

9 then 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.

10 And 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.

11 But if he cannot afford two turtledoves or two young pigeons, he may bring a tenth of an ephah of fine flour as a sin offering. He must not put olive oil or frankincense on it, because it is a sin offering.