Yazīd knew that the military expedition to Medina and the Prophet's (s) shrine, where many of the inhabitants were the Muhājirin and Ansār and the companions of the Prophet (s) would be a difficult task, requiring a confidential and trustable commander.
The historians reported that Yazīd first called upon a person named Dahhāk b. Qays Fihrī1, then 'Amr b. Sa'īd Ashdaq2), and after that 'Ubayd Allāh b. Ziyād3 to carry out this mission. Each one of them, however, rejected this mission, stating that shedding the blood of the descendents of Muhājirin and Ansār and violating the sanctity of the Prophet's (s) shrine was a burden too heavy for them to shoulder.
Finally, this mission was assigned to someone known as Muslim b. 'Uqba and Yazīd entrusted this costly command to him!
Muslim b. 'Uqba was an old man who had lived for more than ninety years and was sick then!468
A person at that age and in that unfavorable physical condition did not seem to be the right option for such a mission. But, apparently it seemed that Yazīd:
Firstly, had to take this option, as the others whom he had selected did not accept the mission.
Secondly, the mission required above all, a commander who was entirely at the service of the Umayyids and deeply devoted to them; and Mu'āwiyah had already talked to Yazīd about Muslim b. 'Uqba and reassured him of his devotedness and loyality to the Umayyids.569
Thirdly, Yazīd had to send someone to the battle against the Muhājirin and Ansār who had no fear of bloodshed and whose physical appearance could be a source of encouragement to the troops.
Although Muslim b. 'Uqba was physically not regarded as a commander powerful enough to stir up the forces by his military gestures, his old age could encourage the naïve and ill-informed troops of Syrian army to invade the sanctity of the Prophet's holy land and fail to view it as an emotionally and religiously vile act.
With these calculations in mind, Yazīd appointed Muslim b. 'Uqba as the commander-in-chief of his army and assigned Husayn b. Numayr Sakūnī, Hubaysh b. Dulja Qīnī, and Rawh b. Zanbā' Jazāmī, each of them to separately command a section of that army.670
Yazīd ordered the government's officials as well as the ordinary people to be encouraged to participate in this conflict.
The state heralds were announcing in the streets and public places:
“O People! Mobilize for fighting against the people of Hijāz and receive your wage!” Whoever volunteered would receive one hundred dinars cash right on the spot. Those for whom only money was important immediately agreed. After a short while about twelve thousand individuals gathered.7
Some other historians have reported the number of Syrian army as amounting to ten thousand troops.
The age span of the troops was between twenty to fifty years. All required equipment had been provided for them, so that many camels were carrying necessary equipment and weapons of the army.872
Some other historians have put it this way: Yazīd ordered people to prepare to go to Hijāz; twenty thousand infantry troops and seven thousand cavalries prepared. Yazīd gave two hundred dinars to the mounted and a hundred dinars to the infantry troops as award and ordered them to move along with Muslim b. 'Uqba.973
Yazīd accompanied Muslim b. 'Uqba and the Syrian army for about half a Farsakh (2.8 km) to see them off.10
Among the army, some Syrian Christians were also seen who had prepared to fight against the people of Medina.11