Midrasz do Kapłańska 5:7

1) (Vayikra 5:7): ("And if his hand cannot attain enough for a lamb, then he shall bring (the offering) of his guilt wherein he has sinned, two turtle-doves, etc.") "his hand": (The implication is that if he does not have the money, he is not told to borrow (for a rich man's offering, even if he has from whom to borrow) and not to ply his trade. If he has a lamb, and he does not have (enough for the food) that it needs (until he reaches Jerusalem), whence is it derived that he should bring a poor man's offering? From "enough for a lamb." "then he shall bring (the offering of his guilt wherein he has sinned, two turtle-doves or two young pigeons,": He must bring two; one does not suffice.

2) (For otherwise I would say:) Does it not follow a fortiori — This one brings what he can afford and a metzora (a leper) brings what he can afford. Just as a metzora brings one (bird sin-offering) for one (lamb sin-offering, and one bird burnt-offering for one bird burnt-offering), this one, too, (in our case), since the rich man brings one (lamb), the poor man should bring one! Therefore, (to negate this) it is written "two turtle-doves or two young pigeons" — he brings two and not one.

3) (Vayikra 5:7) "one for a sin-offering and one for a burnt-offering": (The dedication of) the sin-offering must precede (the dedication of) the burnt-offering. Alternately: that the burnt-offering be of the same species as the sin-offering (turtle-dove or young pigeon, respectively) (and that) if he separated his sin-offering and died, his heirs bring his burnt-offering. Alternately: What is the intent of "one for a sin-offering and one for a burnt-offering?" I might think that since two (birds) are brought in place of a (lamb) sin-offering, they should both be sin-offerings, it is, therefore, written "one for a sin-offering" — and not two; "one for a burnt-offering" — and not two.