al-Harith al-Muhasibi

Abu Abd Allah al-Harith ibn Asad al-Muhasibi (c. 781-857 CE / c. 165-243 AH) was an early Muslim moralist and theologian active in Baghdad. He is best known for his attention to the inner life: his nickname, al-Muhasibi, comes from muhasaba, the practice of taking one's soul to account through rigorous self-examination. Tradition holds he was born in Basra, in southern Iraq, and that his family moved while he was young to Baghdad, the new Abbasid capital, where he spent his working life.

Sources report that he studied law in the circle around al-Shafi'i and later associated with theologians around Ibn Kullab, a milieu that scholars regard as a forerunner of the later Ash'ari school (a tradition of Sunni theology). His major work, al-Ri'aya li-huquq Allah ("Observing the Rights of God"), set out a psychology of devotion and is treated as a foundation for Sufism, the Islamic tradition of inner spiritual discipline. Later Sufi masters such as al-Junayd are remembered as connected to his circle, and his influence on al-Ghazali is widely noted.

His careful use of kalam (rational, dialectical theology) to argue against the Mu'tazila drew sharp criticism from the traditionist Ahmad ibn Hanbal, who held that such reasoning was itself blameworthy. Reports say Ibn Hanbal's followers pressed people to shun al-Muhasibi's lessons, and that only a handful attended his funeral. Whether this rationalist method was legitimate was a contested question, presented here as a dispute between schools rather than settled fact.