听力原文： Born Cassius Clay in Louisville, Kentucky, in 1942, Muhammad Ali retired from boxing in 1980. As an amateur, he won 100 of 108 fights. Later, as a professional boxer, Ali was trained by Angelo Dundee, who pushed him on to face champion boxer Sonny Liston in 1964 in this exciting match, Liston was unable to continue the fight after the sixth round. After winning the championship fight against Liston, Ali announced that he had joined the Black Muslim religion. At the time, the Vietnam War was in progress. When Ali claimed to be a conscientious objector to the war, based on religious grounds, he was denied exemption from military service. Refusing to be inducted into the U. S. Army, he was stripped of his right to box and was given a five-year prison sentence, a conviction that was reversed three years later. Once again able to enter the ring, Muhammad Ali became the first man to win the world' s heavy weight boxing title three times. According to the lecture, what was the result of Ali's 1964 fight against Sonny Liston?