Exodus 11:5-7

and 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 behind the handmill, and all the firstborn of the cattle. There shall be a great cry throughout all the land of Egypt, such as there has never been, nor ever will be again. But not a dog shall growl against any of the people of Israel, either man or beast, that you may know that the LORD makes a distinction between Egypt and Israel.’