Major religious figure of the Umayyad period. Produced writings and sermons that were extremely influential in all areas of Islamic piety, from theology to Quranic exegesis. Known especially for his asceticism and upholding the doctrine of free will and the believer's own responsibility for sin. Often critical of or opposed to Umayyad rulers, but did not approve of rebellion against tyrannical rule. His sermons contain some of the earliest and best examples of Arabic prose style.