Exodus 13:2, 12-15

“Sanctify to Me [that is, set apart for My purpose] every firstborn, the first offspring of every womb among the children of Israel, both of man and of animal; it is Mine.”

you shall set apart and dedicate to the LORD all that first opens the womb. All the firstborn males of your livestock shall be the LORD’S. Every firstborn of a donkey you shall redeem by [substituting] a lamb [as a sacrifice for it], but if you do not [wish to] redeem it, then you shall break its neck; and every firstborn among your sons you shall redeem [that is, ‘buy back’ from God with a suitable sacrifice]. And it shall be when your son asks you in time to come, saying, ‘What does this mean?’ you shall say to him, ‘With a strong and powerful hand the LORD brought us out of Egypt, from the house of bondage and slavery. For it happened, when Pharaoh stubbornly refused to let us go, that the LORD struck every firstborn in the land of Egypt, both the firstborn of man and the firstborn of animal. Therefore, I sacrifice to the LORD all the males, the first [to be born] of every womb, but every firstborn of my sons I redeem.’