Halakhah zu Wajikra 12:6

The law of the sacrifice of the woman that has given birth: That a woman who has given birth bring a sacrifice when the days of her purification for a son or a daughter are completed. And it is a one-year old lamb for a burnt-offering and a young pigeon or a dove for a sin-offering. And if she is poor, she brings two doves or two young pigeons - one for a burnt-offering and one for a sin offering, as it is stated (Leviticus 12:6), "On the completion of the days of purification for a son or daughter, she shall bring, etc." And she is lacking atonement until she brings her sacrifice.