Since the sira is part of the sunnah, or moral example that Muslims are supposed to follow, and validating the sayings of Muhammad is a major study (isnad), accurate biography has always been of great interest to Muslims.
Another important influence of biography on Islam is in the recording of the lives of the four Rightly Guided Caliphs , who expanded Islamic dominance rapidly:
During the 30 years from the death of Muhammad to the death of Ali, Islam had spread from Libya to Afghanistan, from Armenia to Sind and Gujarat, and also in Spain and China. The risk of factional splintering, variant heresies regarding the life of Muhammad, and the gains that local leaders could gain by promoting such division grew to extremes.
Muslim biographers, accordingly, became expert at sorting out facts from accusations, bias from evidence, etc., and were renowned throughout the known world for their honesty in recording history - many in fact considered acknowledging faults in leaders to be a matter of religious duty, comparing their various failings to the sira or life of Muhammad. Modern practices of scientific citation and historical method owe a great deal to the rigor the isnad tradition of early Muslims.