Genesis 26:7-9

7When the men of that place asked him about his wife, he replied, “She is my sister.” He was afraid to say, “She is my wife,” for he thought to himself, “The men of this place will kill me to get Rebekah because she is very beautiful.”

8After Isaac had been there a long time, Abimelech king of the Philistines happened to look out a window and observed Isaac caressing his wife Rebekah.

9So Abimelech summoned Isaac and said, “She is really your wife! Why did you say, ‘She is my sister’?” Isaac replied, “Because I thought someone might kill me to get her.”