Leviticus 5:7-8

7“But if he cannot afford an animal from the flock, then he may bring to the Lord two turtledoves or two young pigeons as penalty for guilt for his sin — one as a sin offering and the other as a burnt offering.

8He is to bring them to the priest, who will first present the one for the sin offering. He is to twist its head at the back of the neck without severing it.