Exodus 12:13

Overview - Exodus 12
1	The beginning of the year is changed.
3	The passover is instituted.
11	The import of the rite of the passover.
15	Unleavened bread, etc.
29	The firstborn are slain.
31	The Israelites are driven out of the land.
37	They come to Succoth.
41	The time of their sojourning.
43	The ordinance of the passover.

Exodus 12:13  (King James Version)
And the blood shall be to you for a token upon the houses where ye are: and when I see the blood, I will pass over you, and the plague shall not be upon you to destroy you, when I smite the land of Egypt.