He enjoyed great favour with Harun-ar-Rashid, who used to declare that he would not refuse him anything. When, however, this Khalif fell ill at Tus, and asked Gabriel for his opinion, the latter replied that if Harun had followed his advice to be moderate in sexual pleasure, he would not have been attacked by the disease.
For this reply he was thrown into prison, and his life was saved only by the chamberlain Rabi'i, who was very fond of him. Amin, the son and successor of Rashid, followed the advice of Gabriel more than his father did, and would not eat or drink anything without his doctor's sanction.
In A.D. 817 Gabriel cured Sehl bin Hasan, who recommended him to Mamun; but Michael, the son-in-law of Gabriel, was his body physician. In A.D. 825 Mamun fell sick, and, as all the medicines of Michael were of no use, Isa, the brother of Mamun, advised him to get himself treated by Gabriel, who had known him from boyhood; but Abu Ishak, the other brother of Mamun, called in Yahya bin Maseweih, and when he could do nothing, then Mamun sent for Gabriel, who restored him to health in three days, and was handsomely rewarded in consequence.
When Mamun marched, in A.D. 828, against the Byzantines, Gabriel fell sick and died, whereon the Khalif took Gabriel's son with him on the campaign, he being also an intelligent and skilled physician.
The works of Gabriel are:
(1) A treatise on food and drink, dedicated to Mamun.
(2) An introduction to logic.
(3) Extracts from medical Pandects.
(4) A book on fumigatories.