Exodus 34:20

every firstling of kine and sheep; but the firstling of an ass thou shalt redeem with a sheep; and if thou wilt not redeem it with that thou shalt pay the worth of it. Every first born of thy sons thou shalt redeem. Thou shalt not appear before me empty.

And the first-born of an ass thou shalt redeem with a sheep, and if thou wilt not redeem it thou shalt pay a price: every first-born of thy sons shalt thou redeem: thou shalt not appear before me empty.