Exodus 12:12-13

12For 1I will go through the land of Egypt on that night, and fatally strike all the firstborn in the land of Egypt, from the human firstborn to animals; and 2against all the gods of Egypt I will execute judgments--3I am the Lord. 134The blood shall be a sign for you on the houses where you 5live; and when I see the blood I will pass over you, and no plague will come upon you 6to destroy you when I strike the land of Egypt.