The pressing danger sobered the Arabs and temporarily united all parties and factions. The army was concentrated at Āmul but for three months was unable to cross the river in the face of the combined native and Türgesh armies. A small body under Qa_t_an b. Qutayba which had already crossed and fortified itself before the arrival of the Turks was beleaguered. The Turkish cavalry even made raids on Khurāsān with an excess of boldness which was punished by a mounted force under Thābit Qu_t_na. At length Ashras got his forces across and, joining with Qa_t_an b. Qutayba, advanced on Paykand. The enemy cut off the water supply, and had it not been for the gallantry and self-sacrifice of _H_ārith b. Surayj, Thābit Qu_t_na, and their companions, an even greater and more irretrievable “Day of Thirst” had resulted. In spite of their weakness, Qa_t_an and the cavalry of Qays and Tamīm charged the enemy and forced them back, so that Ashras was able to continue his advance towards Bukhārā. In the heavy fighting the Muslim forces were divided, Ashras and Qa_t_an gave each other up for lost, and Ghūrak judged that the time had come to throw in his lot with the Turks. Two days later, however, the armies were reunited and on the retiral of the Turks encamped at Bawādara outside the walls of Bukhārā, whence they prepared to besiege the city. Ghūrak also retrieved his error and rejoined Ashras. The Khāqān withdrew towards Samarqand, but sat down before Kamarja, expecting to take it by storm in a few days at the most. The Arabic narratives of these events are confused in several places, which has given rise to many incorrect statements, such as that Ghūrak was beleaguered with the Arabs in Kamarja and that the garrison consisted of Qa_t_an and his forces. Kamarja was not in the neighbourhood of Paykand, as Wellhausen states, but a few farsakhs west of Samarqand[87]. When the garrison would not yield to assault Khāqān tried other methods. Accompanying his expedition was Khusrū the son of Pērōz and grandson of Yazdigird, heir of the Sāsānid kings. This prince was sent to parley with the garrison, but when he claimed the restoration of his kingdom and promised them an amnesty, it is not surprising that the Arabs indignantly refused to hear him. Nor would the appearance of a Sāsānid prince evoke much enthusiasm amongst the Iranians of Transoxania. As the Sāsānid house had taken refuge in China, however, the presence of Khusrū might be taken as an indication that the rebels were receiving encouragement from China also, though the Chinese records are silent on this expedition. Khāqān’s second proposal, that he should hire the Arabs as mercenaries, was rejected as derisively as the first. The siege was then pressed with renewed vigour, both sides putting their prisoners and hostages to death, but after fifty-eight days Khāqān, on the advice of the son of Ghūrak and the other _S_ughdian princes, allowed the garrison to transfer either to Samarqand or Dabūsia.