Leviticus 27:9-13

9And if it shall be a beast, of which men bring an offering to the LORD, all that any man giveth of such to the LORD shall be holy. 10He shall not alter it, nor change it, a good for a bad, or a bad for a good: and if he shall at all change beast for beast, then it and the exchange of it shall be holy. 11And if it shall be any unclean beast, of which they do not offer a sacrifice to the LORD, then he shall present the beast before the priest: 12And the priest shall value it, whether it be good or bad: as thou valuest it, who art the priest, so shall it be.1 13But if he will at all redeem it, then he shall add a fifth part of it to thy estimation.