Exodus 11:4-8

Then Moses said, “This is what the Lord says: ‘About midnight I am going out into the midst of Egypt,

and all the firstborn in the land of Egypt shall die, from the firstborn of the Pharaoh who sits on his throne, to the firstborn of the slave girl who is behind the millstones; all the firstborn of the cattle as well.

So there shall be a great cry in all the land of Egypt, such as there has not been before and such as shall never be again.

But not even a dog will threaten any of the sons of Israel, nor anything from person to animal, so that you may learn how the Lord distinguishes between Egypt and Israel.’

And all these servants of yours will come down to me and bow themselves before me, saying, ‘Go out, you and all the people who follow you,’ and after that I will go out.” And he left Pharaoh in the heat of anger.