Numbers 18:17

but the firstlings of kine, and the firstlings of sheep, and the firstlings of goats, thou shalt not suffer them to redeem. They are hallowed; therefore thou shalt pour out their blood before the altar, and offer their suet as an offering of homage, for a smell of fragrance for the Lord.

But thou shalt not redeem the first-born of calves and the first-born of sheep and the first-born of goats; they are holy: and thou shalt pour their blood upon the altar, and thou shalt offer the fat as a burnt-offering for a smell of sweet savour to the Lord.