Exodus 34:20

20 And the firstling of an ass thou shalt redeem with a lamb: and if thou wilt not redeem it, then thou shalt break its neck. All the first-born of thy sons thou shalt redeem. And none shall appear before me empty.

Exodus 34:20 In-Context

18 The feast of unleavened bread shalt thou keep. Seven days thou shalt eat unleavened bread, as I commanded thee, at the time appointed in the month Abib; for in the month Abib thou camest out from Egypt.
19 All that openeth the womb is mine; and all thy cattle that is male, the firstlings of cow and sheep.
20 And the firstling of an ass thou shalt redeem with a lamb: and if thou wilt not redeem it, then thou shalt break its neck. All the first-born of thy sons thou shalt redeem. And none shall appear before me empty.
21 Six days thou shalt work, but on the seventh day thou shalt rest: in plowing time and in harvest thou shalt rest.
22 And thou shalt observe the feast of weeks, [even] of the first-fruits of wheat harvest, and the feast of ingathering at the year's end.
The American Standard Version is in the public domain.