Exodus 12:24-30

You shall observe this event [concerning Passover] as an ordinance for you and for your children forever. When you enter the land which the LORD will give you, as He has promised, you shall keep and observe this service. When your children say to you, ‘What does this service mean to you?’ you shall say, ‘It is the sacrifice of the LORD’S Passover, for He passed over the houses of the Israelites in Egypt when He struck the Egyptians, but spared our houses.’ ” And the people bowed [their heads] low and worshiped [God]. Then the Israelites went and did [as they had been told]: just as the LORD had commanded Moses and Aaron, so they did. Now it happened at midnight that the LORD struck every firstborn in the land of Egypt, from the firstborn of Pharaoh who sat on his throne to the firstborn of the prisoner who was in the dungeon, and all the firstborn of the cattle. Pharaoh got up in the night, he and all his servants and all the Egyptians, and there was a great cry [of heartache and sorrow] in Egypt, for there was no house where there was not someone dead.