And so we may suppose it to have been with the leading passages in the life of
  the Prophet. His infancy, the Heavenly journey, the deputations from Arab
  tribes, the fields of Bedr, Ohod and Kheibar, his deathbed; each formed,
  apparently, a separate episode, amplified by the rhapsodists who had learned
  the outline. In the course of repetition such episodes gradually acquired a
  shape that symbolised with the spiritual requirements of the day, and, like
  the tale of Antar, became stereotyped; and thus, assuming the form of a
  tradition, were handed down with the usual string of authorities. These
  episodes, Sprenger thinks, were. for the most part not wilful falsehoods, but
  the invention of a "playful fantasy," which filled up with bright
  and suitable colouring the ideal outlines of the Prophet's life. Cast in a
  poetical mould, animated by the dramatic effect of dialogue and sometimes of
  verses put into the speakers' lips, they contain, he thinks, as little basis
  of fact as the mere romances of the pseudo-Wâckidi. Indeed, the narratives
  relating the miracles of Mahomet, which are told with all the gravity of an
  eye-witness, Sprenger designates "as little less than wilful lies."