Genesis 26:8-9

8        And it came to pass, when he had been there a long time, that Abimelech king of the Philistines looked
       out at a window, and saw, and, behold, Isaac was sporting with Rebekah his wife.

9        And Abimelech called Isaac, and said, Behold, of a surety she is thy wife: and how saidst thou, She is my
       sister? And Isaac said unto him, Because I said, Lest I die for her.