Leviticus 27:26-29

26“You may not dedicate a firstborn animal to the Lord, for the firstborn of your cattle, sheep, and goats already belong to him.

27However, you may buy back the firstborn of a ceremonially unclean animal by paying the priest’s assessment of its worth, plus 20 percent. If you do not buy it back, the priest will sell it at its assessed value.

28“However, anything specially set apart for the Lord—whether a person, an animal, or family property—must never be sold or bought back. Anything devoted in this way has been set apart as holy, and it belongs to the Lord.

29No person specially set apart for destruction may be bought back. Such a person must be put to death.