Leviticus 5:7, 9-10

‘If he is not able to bring a lamb, then he shall bring to the LORD, for his trespass which he has committed, two turtledoves or two young pigeons: one as a sin offering and the other as a burnt offering.

Then he shall sprinkle some of the blood of the sin offering on the side of the altar, and the rest of the blood shall be drained out at the base of the altar. It is a sin offering. And he shall offer the second as a burnt offering according to the prescribed manner. So the priest shall make atonement on his behalf for his sin which he has committed, and it shall be forgiven him.