Exodus 34:19-20King James Version (KJV)
19 All that openeth the matrix is mine; and every firstling among thy cattle, whether ox or sheep, that is male.
20 But the firstling of an ass thou shalt redeem with a lamb: and if thou redeem him not, then shalt thou break his neck. All the firstborn of thy sons thou shalt redeem. And none shall appear before me empty.