Exodus 12:12-13

And I will pass through the land of Egypt that night, and will kill every firstborn in the land of Egypt both man and beast: and against all the gods of Egypt I will execute judgments. I am the Lord. And the blood shall be unto you for a sign in the houses where you shall be: and I shall see the blood, and shall pass over you. And the plague shall not be upon you to destroy you, when I shall strike the land of Egypt.