Exodus 12:12-13

For I will go through the land of Egypt in that night, and will strike all the firstborn in the land of Egypt, both man and animal. I will execute judgments against all the gods of Egypt. I am Yahweh. The blood shall be to you for a token on the houses where you are. When I see the blood, I will pass over you, and no plague will be on you to destroy you when I strike the land of Egypt.