Leviticus 27:9-13

9“If your vow involves giving an animal that is acceptable as an offering to the Lord, any gift to the Lord will be considered holy.

10You may not exchange or substitute it for another animal—neither a good animal for a bad one nor a bad animal for a good one. But if you do exchange one animal for another, then both the original animal and its substitute will be considered holy.

11If your vow involves an unclean animal—one that is not acceptable as an offering to the Lord—then you must bring the animal to the priest.

12He will assess its value, and his assessment will be final, whether high or low.

13If you want to buy back the animal, you must pay the value set by the priest, plus 20 percent.