When the Barmakids were deposed and arrested by Caliph Harun al-Rashid in 803, Musa too was imprisoned with his father and brothers until the accession of al-Amin, who released them and showed them again some favour. During the Fourth Fitna, Musa sided with al-Amin, fighting in the ranks of the loyalist army against al-Ma'mun, but he later entered the latter's service. Al-Ma'mun appointed him as governor of Sindh. Musa died in office in 835, and was succeeded by his son, Imran.