Leviticus 27:26-29

26‘However, the firstborn among animals, which as a firstborn belongs to the Lord, no man may consecrate, whether an ox or a sheep. It is [already] the Lord’s.

27If it is among the unclean animals, the owner may redeem it in accordance with your valuation, and add one-fifth to it; or if it is not redeemed, then it shall be sold in accordance with your valuation.

28‘But nothing that a man sets apart [that is, devotes as an offering] to the Lord out of all that he has, of man or of animal or of the fields of his own property, shall be sold or redeemed. Anything devoted to destruction (banned, cursed) is most holy to the Lord.

29No one who may have been set apart among men shall be ransomed [from death], he shall most certainly be put to death.