Exodus 12:12-13

And I will cross through the land of Egypt that night, and I will strike down all the firstborn in the land of Egypt, from man, even to cattle. And I will bring judgments against all the gods of Egypt. I am the Lord. But the blood will be for you as a sign in the buildings where you will be. And I will see the blood, and I will pass over you. And the plague will not be with you to destroy, when I strike the land of Egypt.