Exodus 12:12; Exodus 12:29

12 'For I will go through the land of Egypt on that night, and will strike down all the firstborn in the land of Egypt, both man and beast; and against all the gods of Egypt I will execute judgments -I am the LORD .

29 Now it came about 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 cattle.