the messenger of allâh [pbuh] was then among a small group of fighters — nine in number at the rear of the army[sahih muslim 2/107], watching the engagement and braving the muslim fighters. khalid and his men took him by utter surprise, and obliged him to follow either of two options:

1. to flee for his life and abandon his army to its doomed end, or
   
2. to take action at the risk of his life, rally the ranks of the muslims again and work their way through the hills of uhud towards the encompassed army.

the genius of the messenger of allâh [pbuh], his peerless and matchless courage made him opt for the second course. he raised his voice calling out unto his companions: "slaves of allâh." he did that though he knew that his loud voice would be heard by the idolaters before it was heard by the muslims. he called out unto them risking his life in this delicate situation.

the idolaters, indeed, recognized him and reached his position even before the other muslims could do so.