Exodus 13:12-16

you shall set apart to the LORD all that first opens the womb. All the firstborn of your animals that are males shall be the LORD’s. Every firstborn of a donkey you shall redeem with a lamb, or if you will not redeem it you shall break its neck. Every firstborn of man among your sons you shall redeem. And when in time to come your son asks you, ‘What does this mean?’ you shall say to him, ‘By a strong hand the LORD brought us out of Egypt, from the house of slavery. For when Pharaoh stubbornly refused to let us go, the LORD 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 all the firstborn of my sons I redeem.’ It shall be as a mark on your hand or frontlets between your eyes, for by a strong hand the LORD brought us out of Egypt.”