Exodus 34:18-20

18 a“You shall keep the Feast of Unleavened Bread. Seven days you shall eat unleavened bread, as I commanded you, at the time appointed in bthe month Abib, for in the month Abib you came out from Egypt. 19 cAll that open the womb are mine, all your male
Septuagint, Theodotion, Vulgate, Targum; the meaning of the Hebrew is uncertain
livestock, the firstborn of cow and sheep.
20The efirstborn 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 fnone shall appear before me empty-handed.

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