Leviticus 5:6-7

6He must give a sheep or a goat for a sin offering. Then the Lord will not be angry with him. The priest will kill the animal as a sacrifice to atone for that sin.

7A person may not have money to buy a sheep or a goat. If he does not, he must buy two doves or two pigeons. He must give them to the Lord. One bird will be a sin offering. The second bird will be a burnt offering.