thumb|right|Article II of al-Masihi's Al-Tibb al-Kulli (a treatise on medicine). Copy created in western Iran or Anatolia, dated 1232-3
Abu Sahl 'Isa ibn Yahya al-Masihi al-Jurjani () was a Christian Persian polymath, physician, and philosopher
According to this account, Abū Sahl al-Masīḥī and Avicenna refused to enter Maḥmūd’s service and set out across the Khwarazm desert (Karakum Desert). Avicenna reportedly predicted, on astrological grounds, that they would lose their way, while Abū Sahl foretold that he would not survive the journey. The two men eventually became lost in the desert; Abū Sahl died of thirst, whereas Avicenna, after considerable hardship, reached Abivard and later proceeded to Gurgan. Avicenna composed a short treatise entitled An epistle to Abū Sahl al-Masīḥī on angles (R. ilā Abī Sahl al-Masīḥī fī l-zāwiyah, ') after his departure from Gurgan ("Composed at Jurjān",