Leviticus 5:9 (KJV)

And if he be not able to bring a lamb, then he shall bring for his trespass, which he hath committed, two turtledoves, or two young pigeons, unto the Lord; one for a sin offering, and the other for a burnt offering.

And he shall bring them unto the priest, who shall offer that which is for the sin offering first, and wring off his head from his neck, but shall not divide it asunder:

And he shall sprinkle of the blood of the sin offering upon the side of the altar; and the rest of the blood shall be wrung out at the bottom of the altar: it is a sin offering.

And he shall offer the second for a burnt offering, according to the manner: and the priest shall make an atonement for him for his sin which he hath sinned, and it shall be forgiven him.

But if he be not able to bring two turtledoves, or two young pigeons, then he that sinned shall bring for his offering the tenth part of an ephah of fine flour for a sin offering; he shall put no oil upon it, neither shall he put any frankincense thereon: for it is a sin offering.