Leviticus 12:8

And if she be not able. — As a merciful provision for those who were too poor to bring a lamb, the law permits them to bring a turtle-dove or a pigeon for a burnt offering, provided only it is the same kind of bird as the one brought for a sin offering; that is, they must either be both turtle-doves or both pigeons, and not one turtle-dove and one pigeon. Turtle-doves and pigeons were plentiful and cheap in Palestine (see Leviticus 1:14). It was therefore the poor woman’s sacrifice which the mother of our Lord offered, when, in accordance with this commutation, she offered a pair of turtle-doves or two young pigeons, on presenting herself for purification at the Temple with the child Jesus, on the expiration of the prescribed term of uncleanness (Luke 2:24), and the priest, after sprinkling her with the blood of the humble sacrifice, declared her cleansed.