B'resheet (Gen) 26:8-10

But one day, after he had lived there a long time, Avimelekh king of the P’lishtim happened to be looking out of a window when he spotted Yitz’chak caressing Rivkah his wife. Avimelekh summoned Yitz’chak and said, “So she is your wife, after all! How come you said, ‘She is my sister’?” Yitz’chak responded, “Because I thought, ‘I could get killed because of her.’” Avimelekh said, “What is this you have done to us? One of the people could easily have slept with your wife, and you would have brought guilt on us!”