Leviticus 12:7-8

7The priest will offer the gifts to the Lord. Then the woman will become clean. These are the rules at the birth of a boy or of a girl.

8If the woman does not have money to buy a sheep she can give two doves or pigeons. The priest will use one bird for a sin offering and he will burn the other one. That is how he will make atonement for her. Then she will be clean.’