Exodus 13
14 Ref It shall be, when your son asks you in time to come, saying, 'What is this?' that you shall tell him, 'By strength of hand Yahweh brought us out from Egypt, from the house of bondage;
15 Ref and it happened, when Pharaoh would hardly let us go, that Yahweh killed all the firstborn in the land of Egypt, both the firstborn of man, and the firstborn of animal. Therefore I sacrifice to Yahweh all that opens the womb, being males; but all the firstborn of my sons I redeem.'
16 Ref It shall be for a sign on your hand, and for symbols between your eyes: for by strength of hand Yahweh brought us forth out of Egypt."