Exodus 12:29

29Now 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 12:29 Lit house of a cistern. Cisterns, which were underground water reservoirs, were, when dry, sometimes used to confine prisoners.dungeon, and all the firstborn of the cattle.