Exodus 11:4-6

And Moses said, Thus saith Jehovah, About midnight will I go out into the midst of Egypt: and all the first-born in the land of Egypt shall die, from the first-born of Pharaoh that sitteth upon his throne, even unto the first-born of the maid-servant that is behind the mill; and all the first-born of cattle. And there shall be a great cry throughout all the land of Egypt, such as there hath not been, nor shall be any more.