Exodus 12:12-13

‘I will pass through  the land of Egypt on that night and strike every firstborn male in the land of Egypt, both people and animals. I am the LORD; I will execute judgements against all the gods of Egypt.  The blood on the houses where you are staying will be a distinguishing mark for you; when I see the blood, I will pass over you. No plague will be among you to destroy you when I strike the land of Egypt.