and expense, a Muslim official contrived to get up onto it, and to call the adhan (the Muslim call to prayer) from its walls. This was turned into a pretext to annex the building. Ultimately, Muslim scholars like Al-Biruni found few records left of the belief of for instance the Khawarizmians because figures like Qutayba ibn Muslim "extinguished and ruined in every possible way all those who knew how to write and read the Khawarizmi writing, who knew the history of the country and who studied their sciences." As a result, "these things are involved in so much obscurity that it is impossible to obtain an accurate knowledge of the history of the country since the time of Islam..." Conversion Though subject to a new leadership and harassment, the Zoroastrians were able to continue their former ways, although there was a slow but steady social and economic pressure to convert, with the nobility and city-dwellers being the first to do so, while Islam was accepted more slowly among the peasantry and landed gentry. "Power and worldly-advantage" now lay with followers of Islam, and although the "official policy was one of aloof contempt, there were individual Muslims eager to proselytize and ready to use all sorts of means to do so." In time, a tradition evolved by which Islam was made to appear as a partly Iranian religion. One example of this was a legend that Husayn, son of the fourth caliph Ali and grandson of Islam's prophet Muhammad, had married a captive Sassanid princess named Shahrbanu. This "wholly fictitious figure" was said to have borne Husayn a son, the historical fourth Shi'a imam, who claimed that the caliphate rightly belonged to him and his descendants, and that the Umayyads had wrongfully wrested it from him. The alleged descent from the Sassanid house counterbalanced the Arab nationalism of the Umayyads, and the Iranian national association with a Zoroastrian past was disarmed. Thus, according to scholar Mary Boyce, "it was no longer the Zoroastrians alone who stood for patriotism and loyalty to the past." The "damning indictment" that becoming Muslim was Un-Iranian only remained an idiom in Zoroastrian texts. With Iranian support, the Abbasids overthrew the Umayyads in 750, and in the subsequent caliphate government—that nominally lasted until 1258—Muslim Iranians received marked favor in the new government, both in Iran and at the capital in Baghdad. This mitigated the antagonism between Arabs