Exodus 12:12-13

For I will pass through the land of Egypt this night and will smite all the firstborn in the land of Egypt, both man and beast, and against all the gods of Egypt I will execute judgment. I am the LORD. The blood shall be to you for a sign on the houses where you are. And when I see the blood, I will pass over you, and the plague shall not be upon you to destroy you when I smite the land of Egypt.