Mohammad having accepted the offer, seized upon Sa'b easily, and thanks to the machines he found therein, which he used to destroy the ramparts, he captured the remaining fortresses of Natha, one after the other. They all contained provisions in abundance. While taking one of these forts, the poet Amr ibn u'l-Uhayha, pursuing one of the enemy, dealt him a furious sabre-cut, aiming at his legs to stop him in his flight. But the blade, too short, striking the empty air, rebounded from the force of the blow and pierced Amar's knee, setting up such strong hemorrhage that he expired soon afterwards, being sacrificed by his own hand, whilst fighting for Allah. The most important of all the Khaibar citadels was still standing: that of Al-Qamus, in which Kinana, Prince of the Banu-Nadir, had taken refuge. It was defended by Marhab al-Yahudi, an illustrious warrior. Built on the top of a vertical black rock, with smooth sides, and surrounded by cleverly-designed fortifications, this fort was said to be impregnable. After ten days of desperate efforts against the ramparts, the Believers, however, succeeded in effecting a breach, into which leapt the Prophet, setting the example to his companions; but after having been in the greatest danger, he was compelled to retrace his steps. The shooting pains of neuralgia forcing him to take forty-eight hours' rest, he entrusted the standard to Abu Bakr, who led an attack through the breach, with the most ardent courage, but he also had to beat a retreat at last. Umar took his place, accomplishing prodigies of valour, likewise without success. Hearing of their failure, Mohammad declared: 'By Allah! to-morrow I'll confide the flag to an intrepid fellow, to whom flight is unknown. He loveth Allah and His Messenger, and by them he is beloved. 'Tis he who will capture Al-Qamus by sheer strength.' Next day, all the companions clustering close to the Prophet were anxious to learn who was the man among them to be so greatly honoured. But without glancing at the group, he sent for Ali who had to remain in the rear because he was suffering from painful ophthalmia. Led by a friend, he came into the Prophet's presence. Ali's eyes were covered by a bandage. 'Come hither, close to me,' said Mohammad. 'Take this flag and keep a hold on it until the Almighty shall open a way for thee through these ramparts.'--'I suffer cruelly from my eyes, O Prophet!' replied Ali. 'I cannot even see to walk.' Mohammad made Ali rest his head in his lap; separated the young man's swollen eyelids, and rubbed the bloodshot eyes with a little saliva. All inflammation vanished immediately and every vestige of pain disappeared.... The Prophet then buckled his own breastplate on Ali and armed him with his own sword, celebrated under the title of "Dhu'l-Fiqar".