Exodus 13:15-16

15And it came about, when Pharaoh was stubborn about letting us go, that the 1Lord put to death every firstborn in the land of Egypt, from human firstborns to animal firstborns. Therefore, I sacrifice to the Lord the males, every firstborn of a womb, but every firstborn of my sons I redeem.’ 16So 2it shall 3serve as a sign on your hand and as 4phylacteries 5on your forehead, for with 6a powerful hand the Lord brought us out of Egypt.”