Exodus 13:15-16

15and when Pharaoh refused to let us go, Adonai slew all the firstborn in the land of Egypt, both men and animals. So I sacrifice to Adonai all firstborn males, but I redeem the firstborn of my sons.’

16So it will be like a sign on your hand and like frontlets between your eyes, for by a strong hand Adonai brought us out of Egypt.”