the messenger of allâh [pbuh] mobilized his army. he arranged them into two rows to prepare them for fight. he selected fifty skillful archers that formed a squad and made them under the command of ‘abdullah bin jubair bin an-nu‘man al-ansari al-awsi al-badri. he issued his orders to them to stay where they were — on a mountain(side) at the south bank of qanat al-wadi (i.e. a canal of the valley), south east of muslims camp at about one hundred and fifty metres from the islamic army. later on this mountain was called the mountain of archers.
the messenger of allâh [pbuh] clarified the mission of this squad in words he directed to them. he said to their leader: "drive off the horses from us by means of arrows, lest they should attack us from behind (the rear). whether we win the battle or lose it, stand steadily in your position and mind that we are not attacked from your side."[ibn hisham 2/65,66]
"defend our backs! if you see us slain. do not come to assist us; and if you see gaining grounds, do not share us."[fath al-bari 7/350]
in a version by al-bukhâri the prophet [pbuh] said:
"if you see us snatched into pieces by birds, do not leave this position of yours till i send for you. and if you see that we have defeated the enemy and trodden on them do not desert your position till i send for you."[sahih al-bukhari, the book of jihad 1/426]
with the assignment of this squad and locating it on the mountainside and the issuance of those strict military orders, the messenger of allâh [pbuh] blocked the only groove that might lead the idolaters stealthily to the rear of muslim ranks and might even enable them to encircle them in an encompassment procedure.
the assignments of posts and responsibilities for the rest of the army were performed by the prophet [pbuh] as follows: on the right wing, he appointed al-mundhir bin ‘amr. on the left he appointed az-zubair bin al-‘awwam, and made al-miqdad bin al-aswad his assistant and supporter. az-zubair’s function was to standfast in the face of khalid bin al-waleed’s horsemen. the messenger of allâh [pbuh] selected the top and the most courageous group to be in the vanguard of the army. they were notable for their readiness, alertness and bravery and estimated to be equal to thousands of men.
it was a wise and carefully-laid plan which revealed the genius of military leadership that the prophet [pbuh] possessed. no other leader could have drawn a more accurate or wise plan. although he approached the site later than the enemy, he managed to occupy better positions. he made the rocky mountainside to function as shield for the army’s rear and right flank. he was able, by blocking the only vulnerable gap on the side, to provide additional maximum protection for the rear as well as the left wing. for fear of possible defeat, and to deter the muslims from fleeing, in which case they would fall easy prisoners in the hands of the enemy, he chose a high place for encampment. moreover a strategic site of this sort would surely inflict heavy losses on the polytheists if they thought of approaching or occupying his positions. in a further step, he reduced the enemy to a narrow scope of choice when they were cornered for encampment in geographically low positions that would avail them nothing of the benefits of any possible victory; at the same time they would not be able to escape the pursuit of the muslims in case victory sided with the latter. to make up for the quantitative shortage in fighting personnel, he chose a picked body of fighters to stand at the front.
the army of the prophet [pbuh] was thus fully mobilized on shawwal 7th, 3 a.h.