Numbers 18:15-17

¹⁵Whatsoever is firstborn of all flesh, which they offer to the Lord, whether it be of men, or of beasts, shall belong to thee: only for the firstborn of man thou shalt take a price, and every beast that is unclean thou shalt cause to be redeemed,

¹⁶And the redemption of it shall be after one month, for five sicles of silver, by the weight of the sanctuary. A sicle hath twenty obols.

¹⁷But the firstling of a cow and of a sheep and of a goat thou shalt not cause to be redeemed, because they are sanctified to the Lord. Their blood only thou shalt pour upon the altar, and their fat thou shalt burn for a most sweet odour to the Lord.