Sifrei Bamidbar 149

(Bamidbar 28:27) "And you shall present a burnt-offering as a sweet savor to the L-rd": You sacrifice these aside from those mentioned in Torath Cohanim (Vayikra 27:18). "You say this; but perhaps they are the same as those mentioned there? — Can you say this? Are they similar? You cannot accept the second supposition, but the first — You sacrifice these aside from those mentioned in Torah Cohanim. "two young bullocks, one ram, etc.": If one found bullocks but not rams, or rams but not lambs, I might think that he does not sacrifice any until he finds all. It is, therefore, written "And you shall present a burnt-offering," implying even one. I might then think that even if all are found, (he may present only one). It is, therefore, written (to negate this) "two young bullocks, and one ram, etc."

(Bamidbar 28:31) "Unblemished shall they be for you, and their libations": The libations are being likened to the (sacrificial) animal. Just as the animal is rendered unfit by blemishes, by deficiency or superfluity, so, the libations.