ABSTRACT
WITHtheappearanceofMuhammadthealmostimpenetrable veilthrownovertheprecedingageissuddenlyliftedandwe findourselvesonthesolidgroundofhistoricaltradition.In orderthatthereasonsforthischangemaybeunderstood,itis necessarytogivesomeaccountoftheprincipalsourcesfrom whichourknowledgeoftheProphet'slifeandteachingis derived.
