Method and Sources

Ibn Sa'd's method in composing Al-Tabaqat al-Kubra was characteristic of the best biographical and hadith scholarship of his era: gathering from multiple sources, citing chains of transmission for reported accounts, and preserving both the information and the evidence for it so that readers could evaluate reliability for themselves.

His primary source was his teacher and employer al-Waqidi, whose encyclopedic research on early Islamic history provided the foundation for many of the work's sections. However, Ibn Sa'd did not simply copy al-Waqidi's material: he organized it within his own framework, added material from other sources, and in some areas departed from al-Waqidi's conclusions. His independence from his teacher's material is demonstrated by the sections of the work that draw on sources al-Waqidi did not use.

Ibn Sa'd also conducted his own research through interviewing living scholars and collecting information from the scholarly networks of Baghdad. In the early third century AH, there were still scholars alive who had known the companions' successors directly, and Ibn Sa'd gathered what they remembered. This method of direct collection from living sources gave the work a freshness and immediacy that purely text-based compilations lacked.

The chains of transmission that Ibn Sa'd cites for many of the accounts he preserves are themselves valuable. They allow later hadith scholars to evaluate the reliability of the reports and to cross-reference them with accounts preserved elsewhere. In many cases, Al-Tabaqat al-Kubra is the earliest or the best surviving source for specific reports about companions and early scholars, making the chains of transmission it cites of direct importance for hadith scholarship.

Ibn Sa'd's approach to women in Islamic history is notable by the standards of his time. The work includes a section on the women companions of the Prophet and women scholars of the early period — an inclusion that reflects both the historical importance of women in the early community and Ibn Sa'd's commitment to comprehensive coverage. The biographies of Khadijah, Aisha, Fatimah, and other women companions preserve information that is available from few other sources.

The work's comprehensiveness extended to including figures who were controversial or whose reliability was disputed. Ibn Sa'd did not limit himself to universally praised scholars but recorded information about figures across the spectrum, sometimes noting reservations about specific individuals. This even-handed approach makes the work more valuable as a historical source even as it complicated its use as a guide to whom to trust.