Exodus 12:23; Exodus 11:4–5

23 iFor the Lord will pass through to strike the Egyptians, and when he sees the blood on gthe lintel and on the two doorposts, the Lord will pass over the door and jwill not allow the destroyer to enter your houses to strike you.

So Moses said, Thus says the Lord: wAbout midnight I will go out in the midst of Egypt, and every firstborn in the land of Egypt shall die, from the firstborn of Pharaoh who sits on his throne, even to the firstborn of the slave girl who is xbehind the handmill, and all the firstborn of the cattle.