Exodus 13:14-16

14And it shall be when thy son asketh thee in time to come, saying, What is this? that thou shalt say to him, With a powerful hand Jehovah brought us out from Egypt, out of the house of bondage.

15And it came to pass, when Pharaoh stubbornly refused to let us go, that Jehovah slew all the firstborn in the land of Egypt, both the firstborn of men and the firstborn of cattle: therefore I sacrifice to Jehovah all that breaketh open the womb — being males; and every firstborn of my children I ransom.

16And it shall be for a sign on thy hand, and for frontlets between thine eyes, for with a powerful hand Jehovah brought us forth out of Egypt.