Described as a
mawla of the tribe of
Khath'am, Musa was the son of Mus'ab ibn Rabi', a secretary to the last
Umayyad caliph
Marwan II who later submitted to the Abbasids during the
Abbasid Revolution. He himself appears to have enjoyed close relations with the Abbasid ruling family, having reportedly been a
milk brother to the third caliph
al-Mahdi at
Humayma. During the reign of
al-Mansur (), Musa was appointed on multiple occasions as governor of the Jazira and Mosul. While there he enacted severe taxation policies which led to widespread unrest and earned a lengthy condemnation of his activities in the
Chronicle of Pseudo-Dionysius of Tell-Mahre. Al-Mahdi nevertheless returned him to the same post in 783–784, during which he carried out the caliph's plans to construct an enlargement of the
Friday mosque in Mosul. In 784 Musa was appointed governor of Egypt with jurisdiction over both its military and taxation affairs, and with the task of quelling the ongoing rebellion of
Dihyah ibn Mus'ab in
Upper Egypt. Within a short time of his arrival he seriously alienated a large segment of the population with his large tax increases, including a doubling of the tax on the
faddan and imposing levies on the markets and beasts of burden, and his standing was further harmed after he was accused of accepting bribes. In response, the
Qays and
Yemen Arabs of the
Hawf district united against him and proclaimed a war of resistance, while the infuriated members of the
Fustat jund for their part formed a secret pact with the Hawfis to not fight against them. In the spring of 785 Musa led his armies out against the Hawfis, but in the resulting encounter he was defeated, abandoned by his men and killed by the rebels. ==Notes==