In 1190, he was stationed among a force of Templars at a sewage facility in Jerusalem. The Crusaders had hitherto been searching for a mystical relic known as the Chalice. After discovering that this object was in fact a woman named Adha, two captains and a sergeant named Sadad were sent out to apprehend her at Don Carvaggio's villa.
As this group hastened to the city gates, they were pursued by Altaïr Ibn-La'Ahad, an Assassin keen on rescuing her. In desperation, they raced toward the sewage facility for refuge, where Sadad was ordered by the captains to stay behind at the gate to guard it against the Assassin. This proved futile as Altaïr scaled the wall and invaded on the opposite side of a canal as soon as they entered. While the captains, joined by Qasim as a replacement for Sadad, watched from the other side of the canal, elite Templars poured in on the intruder. One by one, Altaïr slew each of them, leaping at the last with his Hidden Blade. With that, the two captains commanded Qasim to guard Adha with his life before moving closer to the canal to exchange taunts with the Assassin. In response, Altaïr twisted a valve on the wall at his side of the stream. This dramatically increased the pressure in the giant manhole behind the captains; Qasim's commanders perished when they were engulfed by the subsequent toxic explosion.
Beholding the carnage, Qasim defied his last orders and fled the scene, crying that the Assassin "was not a man, but the Devil himself!"