Leviticus 27:9-13

“If he vowed an animal that is acceptable as an offering to GOD, the animal is given to GOD and becomes the property of the Sanctuary. He must not exchange or substitute a good one for a bad one, or a bad one for a good one; if he should dishonestly substitute one animal for another, both the original and the substitute become property of the Sanctuary. If what he vowed is a ritually unclean animal, one that is not acceptable as an offering to GOD, the animal must be shown to the priest, who will set its value, either high or low. Whatever the priest sets will be its value. If the owner changes his mind and wants to redeem it, he must add twenty percent to its value.