Now these views appear erroneous and
  misleading in several respects. They altogether ignore the merit and value of
  the Biographers, which in other places are fully admitted by Sprenger himself.
  It is not the case that their works are entirely composed of legend and
  romance, to the exclusion, or nearly so, of fact. The marriage of Mahomet, the
  birth of his daughters, the persecution and consequent flight to Abyssinia,
  the Prophet's "lapse," the long-continued ban and its cancelment,
  the death of Khadîja and Abu Tâleb, the marriage with Sauda and betrothal to
  Ayesha, the visit to Tâyif, the meeting with the citizens of Medina and the
  contract made with them;surely these and many other incidents, all prior to
  the Flight, are based on fact and not on fiction. The truth appears to be that
  the Biographers made use of whatever material they found to their hand, and,
  free from the shackles of the Sunna, they adopted the current legends
  and marvellous episodes with the rest; but, far from confining themselves to
  these, they constrained into their service every kind of tradition pertinent
  to their subject: and it is thus that Wâckidi and his Secretary are specially
  commended elsewhere by Sprenger, for their diligence in the collection of
  traditions, and care in verifying them by the requisite authorities. Like the
  whole race of early Mahometan writers, the Biographers endeavoured (and that
  not seldom by questionable means) to glorify Mahomet and magnify Islam; but
  there is no reason to doubt that otherwise they sought honestly to give a true
  picture of the Prophet; that while they admit some legendary tales excluded
  from the Sunna, their work's are to a very great extent composed of precisely
  the same material; and that they are, moreover, less under the influence of
  theological bias than were the collectors of the  Sunna.