The vicious caliph was scared of the Holy Imam’s (A.S.) increasing publicity and popularity. There was a rapid spread of Shi’ism, a growth in the attachment of the populace to the Holy Imam (A.S.). Ma’mun sought to find a remedy for this difficulty and decided to martyr the Holy Imam (A.S.).
In 203 A.H./ 818 A.D., Mamun set out for Baghdad and asked Imam Reza (A.S.) to accompany him. At Sarakhs, he assassinated Fazl ibn Sahl, the famous minister and commander of the civil military forces of the Abbasid caliphate.