Leviticus 27:9-13

9"If the vow is an animal that may be offered as an offering to the Lord, all of it that he gives to the Lord is holy.

10He shall not exchange it or make a substitute for it, good for bad, or bad for good; and if he does in fact substitute one animal for another, then both it and the substitute shall be holy.

11And if it is any unclean animal that may not be offered as an offering to the Lord, then he shall stand the animal before the priest,

12and the priest shall value it as either good or bad; as the priest values it, so it shall be.

13But if he wishes to redeem it, he shall add a fifth to the valuation.