Numbers 18:14-17

¹⁴Every thing devoted in Israel shall be thine.

¹⁵Every thing that openeth the matrix in all flesh, which they bring to the LORD, whether of men or beast, shall be thine: nevertheless, the first born of man shalt thou surely redeem, and the firstling of unclean beasts shalt thou redeem.

¹⁶And those that are to be redeemed from a month old shalt thou redeem, according to thy estimation, for the money of five shekels, after the shekel of the sanctuary, which is twenty gerahs.

¹⁷But the firstling of a cow, or the firstling of a sheep, or the firstling of a goat, thou shalt not redeem; they are holy: thou shalt sprinkle their blood upon the altar, and shalt burn their fat for an offering made by fire, for a sweet savor to the LORD.