Leviticus 27:26-27
26 “‘No one, however, may dedicate the firstborn of an animal, since the firstborn already belongs to the Lord; whether an ox or a sheep, it is the Lord’s.
27 If it is one of the unclean animals, he may buy it back at its set value, adding a fifth of the value to it. If he does not redeem it, it is to be sold at its set value.