Numbers 18:15 (KJV)

And whatsoever is first ripe in the land, which they shall bring unto the Lord, shall be thine; every one that is clean in thine house shall eat of it.

Every thing devoted in Israel shall be thine.

Every thing that openeth the matrix in all flesh, which they bring unto the Lord, whether it be of men or beasts, shall be thine: nevertheless the firstborn of man shalt thou surely redeem, and the firstling of unclean beasts shalt thou redeem.

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

But 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 savour unto the Lord.