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.