the outward events of his life, so that here we have materials of unique and incontestable authority for tracing the origin and early development of Islam--such materials as do not exist in the case of Buddhism or Christianity or any other ancient religion. Unfortunately the arrangement of the Koran can only be described as chaotic. No chronological sequence is observed in the order of the Súras (chapters), which is determined simply by their length, the longest being placed first.[274] Again, the chapters themselves are sometimes made up of disconnected fragments having nothing in common except the rhyme; whence it is often impossible to discover the original context of the words actually spoken by the Prophet, the occasion on which they were revealed, or the period to which they belong. In these circumstances the Koran must be supplemented by reference to our second main source of information, namely, Tradition. [Sidenote: 2. Tradition (Ḥadíth).] [Sidenote: Biographies of Muḥammad.] [Sidenote: General collections.] [Sidenote: Commentaries on the Koran.] Already in the last years of Muḥammad's life (writes Dr. Sprenger) it was a pious custom that when two Moslems met, one should ask for news (_ḥadíth_) and the other should relate a saying or anecdote of the Prophet. After his death this custom continued, and the name _Ḥadíth_ was still applied to sayings and stories which were no longer new.[275] In the course of time an elaborate system of Tradition was built up, as the Koran--originally the sole criterion by which Moslems were guided alike in the greatest and smallest matters of public and private interest--was found insufficient for the complicated needs of a rapidly extending empire. Appeal was made to the sayings and practice (_sunna_) of Muḥammad, which now acquired "the force of law and some of the authority of inspiration." The Prophet had no Boswell, but almost as soon as he began to preach he was a marked man whose _obiter dicta_ could not fail to be treasured by his Companions, and whose actions were attentively watched. Thus, during the first century of Islam there was a multitude of living witnesses from whom traditions were collected, committed to memory, and orally handed down. Every tradition consists of two parts: the text (_matn_) and the authority (_sanad_, or _isnád_), _e.g._, the relater says, "I was told by _A_, who was informed by _B_, who had it from _C_, that the Prophet (God bless him!) and Abú Bakr and ‘Umar used to open prayer with the words 'Praise to God, the Lord of all creatures.'" Written records and compilations were comparatively rare in the early period. Ibn Isḥáq († 768 A.D.) composed the oldest extant Biography of the Prophet, which we do not possess, however, in its original shape but only in the recension of Ibn Hishám († 833 A.D.). Two important and excellent works of the same kind are the _Kitábu ’l-Maghází_ ('Book of the Wars') by Wáqidí († 822 A.D.) and the _Kitábu