After the assassination of Uthman Ibn Affan, the people’s allegiance to Imam Ali (‘a) is recognized as the most crucial factor in the transfer of power and the beginning of a new era in Islamic history. This allegiance not only led to a change in Islamic leadership but also caused seditions and social tensions among Muslims. Two reliable sources in this regard are Tarikh-i Tabari and Nahj al-Balaghah, which have analyzed the various aspects of this event. Tarikh-i Tabari, as a fundamental source in Islamic historiography, has had a profound impact on historical narratives and future research in this field. This study examines the similarities and differences between these two texts about the pledge of allegiance to Imam Ali (‘a). Both sources emphasize the importance of allegiance and the influence of social and political pressures at the time of the allegiance. Also, Imam Ali’s (‘a) advice and support for Uthman and its impact on the legitimacy of the allegiance are considered in both texts. However, Tarikh-i Tabari elaborates on the details of the events and the social context of the allegiance and analyzes the disagreements. ‘Abdullah Ibn Saba is introduced as a controversial figure in inciting people to allegiance and a factor in the emergence of internal tensions and disputes. The role of the Egyptians in the formation of the uprisings is also clearly highlighted in Tarikh-i Tabari, while events are analyzed differently in Nahj al-Balaghah