Exodus 12:7

12:7 They will take some of the blood and put it on the two side posts and top of the doorframe of the houses where they will eat it.

Exodus 12:13

12:13 The blood will be a sign for you on the houses where you are, so that when I see the blood I will pass over you, and this plague will not fall on you to destroy you when I attack the land of Egypt.

Exodus 12:23

12:23 For the Lord will pass through to strike Egypt, and when he sees the blood on the top of the doorframe and the two side posts, then the Lord will pass over the door, and he will not permit the destroyer to enter your houses to strike you.