Exodus 11:4-7

4So Moses said, “This is what the Lord says: About midnight I will go throughout Egypt,

5and every firstborn male in the land of Egypt will die, from the firstborn of Pharaoh who sits on his throne to the firstborn of the servant girl who is at the grindstones, as well as every firstborn of the livestock.

6Then there will be a great cry of anguish through all the land of Egypt such as never was before or ever will be again.

7But against all the Israelites, whether people or animals, not even a dog will snarl, so that you may know that the Lord makes a distinction between Egypt and Israel.