Musa b. Shakir was not the name of a person to be remembered among the men of letters, religious scholars, or people of knowledge in his youth, but as a bandit who waylaid caravans on the roads of Khurasan. He had placed an operative agent for him who watched out for caravans and informed him of their number and the probable time of their arrival or departure. His modus operandi followed the routine of attending evening prayers in the local Mosque before he embarked on his looting sprees under cover of the night, military uniform on the body and a Veil on his face; he would also see that he returned before dawn and attended prayers in the same Mosque. After sometime, an index of suspicion was raised against him; however, people in the local Mosque were the first to defend him and stated that he attended the evening prayers and was among the earliest to arrive before dawn.
Musa b. Shakir reformed later in his life, possibly at the instance of the Abbasid Caliph al-Ma’mun, and worked in astrologyat his court, long before the latter assumed the august office. He stayed in Marw region of Khurasan, present day Iran, ruled by al-Ma’mun then; after the latter claimed the caliphate in Baghdad, Musa b. Shakir shifted his family to Baghdad where he became a member of the royal retinue. Foreseeing his death, Musa entrusted the guardianship of his sons (Ahmad, Hasan & Mohamad) to the Caliph.