Midrash su Numeri 8:12

2) R. Yossi Haglili says (in connection with Bamidbar 8:8: "And they [the Levites] shall take a young bullock" [for a burnt-offering], "… and a second young bullock shall you take for a sin-offering"): What is the intent of "a second young bullock, etc."? Is it not already written (Bamidbar 8:12): "And you shall make the one a sin-offering, and the other, a burnt-offering to the L–rd"? Why, then, repeat "And a second, etc."? The intent of "second" is "of the second year."

3) Rebbi says: What is the intent of: "and a second young bullock shall you take for a sin-offering"? If to teach that they are two, it is already written: "And you shall make the one a sin-offering, and the other, a burnt-offering to the L–rd." But, because it is written: "And you shall make the one a sin-offering, and the other, a burnt-offering to the L–rd," I might think that the sin-offering takes precedence to the burnt-offering in all of its particulars; it is, therefore, written: "and a second young bullock shall you take for a sin-offering." If that alone were written, I would think that the burnt-offering takes precedence to the sin-offering in all of its particulars; it is, therefore, written: "And you shall make the one a sin-offering, and the other, a burnt-offering to the L–rd." How is this to be reconciled. The (sprinkling of) the blood of the sin-offering takes precedence to that of the burnt-offering, because it effects conciliation. The (burning of the) limbs of the burnt-offering takes precedence to the (burning of the) devoted portions of the sin-offering because all of them are burnt.

4) R. Shimon says: What is the intent of: "and a second young bullock shall you take for a sin-offering"? If to teach that they are two, is it not already written: "And you shall make the one a sin-offering, and the other, a burnt-offering to the L–rd"? — I might think that this sin-offering is to be eaten; it is, therefore, written: "and a second bullock" — second to the burnt-offering. Just as a burnt-offering is not eaten, so this sin-offering is not eaten."