Exodus 12:12-14, 23

“On that same night I will pass through Egypt and strike down every firstborn of both people and animals, and I will bring judgment on all the gods of Egypt. I am the LORD. The blood will be a sign for you on the houses where you are, and when I see the blood, I will pass over you. No destructive plague will touch you when I strike Egypt. “This is a day you are to commemorate; for the generations to come you shall celebrate it as a festival to the LORD—a lasting ordinance.

When the LORD goes through the land to strike down the Egyptians, he will see the blood on the top and sides of the doorframe and will pass over that doorway, and he will not permit the destroyer to enter your houses and strike you down.