‏ Exodus 13:14-15

14 aAnd when in time to come your son asks you, ‘What does this mean?’ you shall say to him, bBy a strong hand the Lord brought us out of Egypt, from the house of cslavery. 15For when Pharaoh stubbornly refused to let us go, the dLord killed all the firstborn in the land of Egypt, both the firstborn of man and the firstborn of animals. Therefore I sacrifice to the Lord all the males that first open the womb, but eall the firstborn of my sons I redeem.’
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