At about the middle of the month of Safar, in the 11th A.H., on Monday, Muhammad ordered his followers to make speedy preparations for an expedition against the people of Mauta in the Byzantine territory, and the sources go to say, to avenge the massacre of the soldiers, who had fallen in recent skirmishes. The next day, on Tuesday he appointed Osama to the command of the army. Osama was the son of Zaid bin Harith, who had been slain at Mauta, and was a youth of 17 or 18 years. On Wednesday, a violent inroad of headache and fever seized Muhammad, but the next morning of Thursday, he found himself sufficiently recovered to prepare a flag-staff, with his own hands, which he made over to Osama. The camp was then erected at Jorf, three miles from Medina on the route to Syria. He ordered all his followers at Medina to join it at once, not excepting even the renowned companions to join it at once. Only Ali, who was required to remain with him at Medina, was exempted. The malady, although gaining ground, did not confine Muhammad entirely to his house. He used to move into the mosque, through the door of his apartment, to lead the prayers. After about a week of his summoning the men to the Syrian expedition under Osama, he perceived that the progress to join the camp at Jorf was very slow and poor, therefore, he once again addressed the people to join the Syrian expedition. The sickness of Muhammad was increasing every day, and the Syrian expedition, weighed upon his mind, and continued saying to those around him, "Send off quickly the army of Osama." According to the Shiites, Muhammad was really reprimanding his companions for not joining the expeditionary force. Knowing that Muhammad's end was near, the companions were reluctant to leave Medina at such a critical time and fearful that, if they absented themselves, Ali might step uncontested. In sum, the army of Osama could not depart from Medina during the time of Muhammad.
According to the Sunni historians, the expedition under Osama was ordered by Muhammad for taking revenge of Osama's father, Zaid bin Harith who had been killed at the hands of the Byzantine force in the battle of Mauta. This view however seems hardly plausible, because the battle of Mauta took place in the year 8/629 and there is no reason why the idea of revenge did not occur earlier 2 two years and 7 months after that event. Secondly, Zaid bin Harith was not the only notable martyr of that battle. Muhammad's cousin, Jafar Taiyar was also killed in the same battle and if the expedition under Osama had been for avenging the blood of Osama's father, Zaid bin Harith, it should as well be for avenging the blood of Jafar Taiyar. But, it is learnt that not only Jafar's real brother, Ali but all other members of Banu Hashim had been expressly detained from joining the expedition under Osama. This indicates clearly that the expedition was not for avenging any one's blood. The critical examination of the sources leads to the conclusion that Muhammad aimed at keeping Ali and his faithfuls in Medina and to keep all others away from the city, so that in the event of his death, Ali could establish himself as the successor of Muhammad without opposition.