Al-Fadl ibn Sahl

Abu l-Abbas al-Fadl ibn Sahl ibn Zadhanfarukh al-Sarakhsi (Arabic: أبو العباس الفضل بن سهل بن زادانفروخ السرخسي‎‎; Abu ’l-ʿAbbās al-Faḍl b. Sahl b. Zādānfarrūḫ as-Saraḫsī, died 818), titled Dhu 'l-Ri'āsatayn ("the man of the two commands"), was a famous Persianvizier of the Abbasid era in Khurasan, who served under Caliph al-Ma'mun (r. 813–832). He played a crucial role in the civil war between al-Ma'mun and his brother al-Amin (r. 809–813), and was the de facto ruler of the Caliphate until 817.

Fadl's father Sahl was a Zoroastrian from Kufa, who later converted to Islam and joined the Barmakids. At the urging of Barmakid Yahya ibn Khalid, Fadl also converted to Islam, probably in 806, and entered the service of the Caliph Harun al-Rashid and his son al-Ma'mun.

Fadl realized very early on that after Harun al-Rashid's death, his throne was disputed between his sons, and urged al-Ma'mun, the son of a Persian concubine, to accompany his father on his expedition to Khurasan, to secure a power-base in Iranian lands. When the arrived events as accurately as Fadl had predicted it, al-Ma'mun made him his chief adviser, and his right hand during the civil war with his brother al-Amin.

After defeating al-Amin, al-Ma'mun became the new Caliph throughout the eastern Islamic world, primarily the Iranian lands, and Fadl was appointed vizier and Emir of these areas. Because of his local role as civil and military leader he received the honorary title of ذو الرئاستين, meaning "the dual leadership of violence". In addition, he was rewarded with immense riches and an inheritable estate. Fadl's brother, al-Hasan ibn Sahl was also appointed Minister of Finance.

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