Leviticus 27:32-34

³²And every tithe of oxen, and of sheep, and whatsoever may come in numbering under the rod, the tenth shall be holy to the Lord.

³³Thou shalt not change a good for a bad, or a bad for a good; and if thou shouldest at all change it, its equivalent also shall be holy, it shall not be redeemed.

³⁴These are the commandments which the Lord commanded Moses for the sons of Israel in mount Sina.