Exodus 13:14-16

14“In days to come, when your son asks you, ‘What does this mean?’ say to him, ‘With a mighty hand the Lord brought us out of Egypt, out of the land of slavery. 15When Pharaoh stubbornly refused to let us go, the Lord killed the firstborn of both people and animals in Egypt. This is why I sacrifice to the Lord the first male offspring of every womb and redeem each of my firstborn sons.’ 16And it will be like a sign on your hand and a symbol on your forehead that the Lord brought us out of Egypt with his mighty hand.”