Hisham ibn Muhammad al-Kalbi (d. 206), the author of Adyan al-Arab, is the first to write in this field as stated by Ibn al-Nadim in Al-Fihrist. Then comes al-Hasan ibn Musa al-Nawbakhti the prominent second century philosopher who wrote Kitab al-Ara’ wa al-Diyanat and Kitab al-Firaq. He preceded people like Abu Mansur Abdulqadir ibn Tahir al-Baghdadi (d. 429), Abu Bakr al-Baqillani (d. 403), Ibn Hazm (d. 456), Ibn Furak al-Isfahani (d. 451), Abu al-Muzaffar Tahir ibn Muhammad al-Isfarani, who died about the same time as al-Isfahani, and al-Shahristani (d. 548). I am not aware of any one who preceded these people in writing about this discipline except al-Kalbi and al-Hasan ibn Musa al-Nawbakhti. Ibn al-Nadim, al-Najashi and others have mentioned them and their works on Islamic sects in the chapter about biographies. We have in our possession a copy of Kitab al-Firaq which is about Shi’ah sects.

Those five authors have been preceded by other Shi’ah writers on Islamic sects some of whom are; Nasr ibn al-Sabah, the teacher of Abu Amr al-Kashshi, the writer on biographies of narrators. The former compiled Kitab Firaq al-Shi’ah. Abu al-Muzaffar Muhammad ibn Ahmad al-Na’imi had a book with the same title. Abu al-Hasan Ali ibn al-Husayn al-Mas’udi (d. 346), the author of Kitab al-Maqalat fi Usul al-Diyanat and Kitab al-Ibanah fi Usul al-Diyanat. He was among the leading Shi’ah scholars as stated by Sheikh al-Tusi in his Fihrist and al-Najashi in Kitab Asma’ al-Musannifin min al-Shi’ah (Biography of Shi’ah Authors). They both ascribe to him Kitab al-Bayan fi Asma’ al-A’immah and Kitab Ithbat al-Wasiyyah fi Imamat al-A’immat al-Ithna Ashar.

Tajal-Din al-Subki is mistaken in claiming that al-Mas’udi was a Shafi’i just as he was mistaken in regarding the chief of the Shi’ah, Sheikh al-Tusi (may both of them rest in peace) as one of them. I have recorded his detailed biography in the original version of this book.