Intelligent Prisoner

Ḥaarith ibn ‛Abbaad, one of the rulers of Al-Andalus (Muslim Spain), was looking to capture ‛Adi ibn Abi Rabi‛ah in order to exact revenge from him. His problem, and that of many of his guards, was that they didn't know what Ibn Abi Rabi‛ah looked like. A prisoner said to one of the guards, "Will you free me if I show you to him?" He (the guard) said, "Yes, I promise to do so." After an oath from him, he said, "I am ‛Adi ibn Abi Rabi‛ah." And, remembering his promise and oath, the guard felt compelled to free him