Now the blood shall be a sign for you on the houses where you are. And when I see the blood, I will pass over you; and the plague shall not be on you to destroy you when I strike the land of Egypt.
Exodus 12:13
Surrounding context
12:12 "For I will pass through the land of Egypt on that night, and will strike 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.
12:13 Now the blood shall be a sign for you on the houses where you are. And when I see the blood, I will pass over you; and the plague shall not be on you to destroy you when I strike the land of Egypt.
12:14 "So this day shall be to you a memorial; and you shall keep it as a feast to the LORD throughout your generations. You shall keep it as a feast by an everlasting ordinance.