Exodus 11:4-6

4So Moses said, “Thus says the Lord: a‘About midnight I will go out in the midst of Egypt, 5and every firstborn in the land of Egypt shall die, from the firstborn of Pharaoh who sits on his throne, even to the firstborn of the slave girl who is bbehind the handmill, and all the firstborn of the cattle. 6 cThere shall be a great cry throughout all the land of Egypt, such as there has never been, nor ever will be again.

Exodus 12:29-30

The Tenth Plague: Death of the Firstborn

29 dAt midnight the eLord struck down all the firstborn in the land of Egypt, ffrom 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 the livestock. 30And Pharaoh rose up in the night, he and all his servants and all the Egyptians. And there was ga great cry in Egypt, for there was not a house where someone was not dead.
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