Leviticus 27:8-10

American Standard Version

⁸ But if he be poorer than thy estimation, then he shall be set before the priest, and the priest shall value him; according to the ability of him that vowed shall the priest value him.

⁹ And if it be a beast, whereof men offer an oblation unto Jehovah, all that any man giveth of such unto Jehovah shall be holy. ¹⁰ He 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 both it and that for which it is changed shall be holy.