William Muir,
The Caliphate: Its Rise, Decline and Fall…
“ Yet to this unscrupulous agent—well named The Sword of God—was due, more than to any other, the survival and the triumph of Islam. But Abu Bekr was not wanting in firmness when stern occasion called; for example, the despatch of Usama's army when Medina lay defenceless and all around was dark showed a boldness and steadfastness of purpose that, more than anything else, helped to roll back the tide of rebellion and apostasy.Faith in Mohammad, secret of his strength. ”
