Exodus 13:2, 12-15

Consecrate to me every firstborn; whatever opens the womb among the Israelites, whether of human being or beast, belongs to me.

you will dedicate to the LORD every newborn that opens the womb; and every firstborn male of your animals will belong to the LORD. Every firstborn of a donkey you will ransom with a sheep. If you do not ransom it, you will break its neck. Every human firstborn of your sons you must ransom. And when your son asks you later on, ‘What does this mean?’ you will tell him, ‘With a strong hand the LORD brought us out of Egypt, out of a house of slavery. When Pharaoh stubbornly refused to let us go, the LORD killed every firstborn in the land of Egypt, the firstborn of human being and beast alike. That is why I sacrifice to the LORD every male that opens the womb, and why I ransom every firstborn of my sons.’