Exodus 34:18–20

18 c“You shall keep the Feast of Unleavened Bread. Seven days you shall eat unleavened bread, as I commanded you, at the time appointed in dthe month Abib, for in the month Abib you came out from Egypt. 19 eAll that open the womb are mine, all your male2 livestock, the firstborn of cow and sheep. 20 The ffirstborn of a donkey you shall redeem with a lamb, or if you will not redeem it you shall break its neck. All the firstborn of your sons you shall redeem. And gnone shall appear before me empty-handed.