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.