According to orientalist professor Etan Kohlberg, Twelver Shia believed in the distortion of the Quran up to the era of the Buyids,[1] and this belief was common among Shia during the early Islamic centuries.[2] Kohlberg claims that Ibn Babawayh was the first major Twelver author "to adopt a position identical to that of the Sunnis".[10] This change in belief was primarily a result of the Shia "rise to power at the centre of the Sunni 'Abbasid caliphate," whence belief in the corruption of the Quran became untenable vis-a-vis the position of Sunni “orthodoxy”.[11] Among other reasons, the distortion was alleged to have been carried out to remove any references to the rights of Ali and the Imams,[12] the approval of their supporters and the disapproval of their enemies, such as specific Umayyads and Abbasids.[13] According to William St. Clair Tisdall, if such content had existed in the Quran then "Of course the Sunnite Khalifahs had very great reason to endeavour to suppress any such passages".[7]