the pride of the byzantine state made it deny muslims their right to live. the byzantine arrogance made them even kill those agents of theirs, who embraced islam. killing farwah bin ‘amr al-judhami, who was their agent on mu’an, was an evidence of their arrogance. due to that arrogance and presumptuousness of the byzantines, the messenger of allâh [pbuh] started to mobilize a great army in safar in the eleventh year of al-hijra and made it under the command of osamah bin zaid bin haritha with orders to have the horses of muslims tread on the lands bordering al-balqa’ and ad-darum of palestine. his aim was to terrorize byzantines and to implant confidence into the hearts of arabs who were settled at the borders of the byzantines. his other purpose was to deliver a message to everybody there, so that no one may dare say that the church brutality can’t go with impunity; and that islamization is not synonymous with fear and vulnerability.

the leadership of osamah was subject to criticism. because he was still too young, people tarried at joining his expedition. the messenger of allâh [pbuh] addressed people saying: 

"no wonder now you contest his leadership, for you have already contested the ex-leadership of his father. yes, by allâh, his father, who was one of the most beloved people to me, was quite efficient for leadership; and this son of his is one of the most beloved individuals to me after his father." [sahih al-bukhari 2/612]

so people started tending towards osamah and joined his army. the number of volunteers in his army was so enormous that they formed such a long queue that they had to descend the escarpment — which was a parasang off madinah. the anxiety-provoking news about the messenger of allâh’s sickness, however, made the expedition tarry again in order to know what allâh had willed as regards his messenger [pbuh].

it was allâh’s will that osamah’s expedition would be the first one dispatched during the caliphate of the veracious abu bakr. [ibn hisham 2/560, 606; sahih al-bukhari 2/612]