Exodus 12:24-30

And you shall observe this thing as an ordinance for you and your sons forever. It will come to pass when you come to the land which the LORD will give you, just as He promised, that you shall keep this service. And it shall be, when your children say to you, ‘What do you mean by this service?’ that you shall say, ‘It is the Passover sacrifice of the LORD, who passed over the houses of the children of Israel in Egypt when He struck the Egyptians and delivered our households.’ ” So the people bowed their heads and worshiped. Then the children of Israel went away and did so; just as the LORD had commanded Moses and Aaron, so they did. And it came to pass at midnight that the LORD struck all the firstborn in the land of Egypt, from the firstborn of Pharaoh who sat on his throne to the firstborn of the captive who was in the dungeon, and all the firstborn of livestock. So Pharaoh rose in the night, he, all his servants, and all the Egyptians; and there was a great cry in Egypt, for there was not a house where there was not one dead.