It is reported that when Jaʿfar al-Barmakī resolved to place al-Faḍl in the service of al-Maʾmūn, he praised him in the presence of Hārūn al-Rashīd. Al-Faḍl then spoke, and al-Rashīd found him quick-witted and eloquent.

He was nicknamed Dhū al-Riʾāsatayn—“the Man of the Two High Offices”—because he simultaneously bore the responsibilities of the vizierate and of the army.

A Shiʿite by persuasion, an astrologer, and a cunning strategist, he was the one who advised that Tāhir ibn al-Ḥusayn be dispatched, and through sand-divination (ʿilm al-raml) he predicted that Tāhir would defeat al-Amīn.

Among his false prognostications, it is said, was his ruling for himself that he would live forty-eight years and would then be killed between water and fire. So it came to pass: he lived exactly that span, and al-Maʾmūn’s maternal uncle slew him in the bathhouse of Sarakhs, in Shaʿbān of the year 202 AH.

The leading poets lavished praise upon him; among them was Ibrāhīm al-Ṣūlī, who composed:
“Al-Faḍl ibn Sahl owns a hand
before which every comparison falls short;
its bounty enriches,
its might decides fate;
its hidden side is generosity,
its manifest side is favors and kisses.” (1)

His stature kept rising until his influence became burdensome for al-Maʾmūn. The caliph therefore sent against him his uncle, Ghālib al-Aswad, with a band of men, and they killed him (2). A few days later his father also died.

Al-Maʾmūn outwardly grieved over his death, consoled his mother, and said, “Allah has given you, in place of your son, myself.”

She wept and replied, “How could I not mourn a son who has gained me a son like you?”

She lived on to witness the wedding of her granddaughter Būrān to al-Maʾmūn (3).

Al-Ḥasan ibn Sahl, for his part, was counted among the eminent and highly commended viziers.