A member of a Soghdian family from Usrushana, Abi'l-Saj entered into the service of the Abbasids and fought under the Afshin during the latter's final campaign against the rebel Babak Khorramdin in 837 AD. He also fought against the Karenid rebel Mazyar in 839, and one year later against Mankjur al-Farghani, the lieutenant and cousin of Afshin. Over the next several decades he served the caliphs in various provinces. In 865 he sided with the caliph al-Musta'in during the civil war of that year, and was put in charge of the defense of al-Mada'in. In the 870s he was sent to Khuzistan to battle the Zanj rebels. However, during his stay in Ahvaz, his brother-in-law 'Abd al-Rahman was killed by the Zanj during a battle, which forced Abi'l-Saj to leave Ahvaz before the Zanj rebels entered the city.
In 876 Abi'l-Saj joined the Saffarid amir Ya'qub bin Layth, who had led his army into Khuzistan during his advance into Iraq against the caliph. He was present during the Battle of Dayr al-'Aqul, which ended in a Saffarid defeat, and reportedly remonstrated Ya'qub after the battle for his bad tactics. Following the defeat, the caliphal regent al-Muwaffaq seized his properties in Iraq. In 879, Ya'qub died after of colic disease, and was succeeded by his younger brother Amr ibn al-Layth, who made peace with the Abbasid Caliphate.
After having made peace with the caliph, Abi'l-Saj left Fars for Baghdad, but died at Gundeshapur in November-December before he managed to reach Baghdad. His two sons, Muhammad and Yusuf, would both go on to have distinguished careers, becoming the first and third, respectively, Sajid governors of Azerbaijan.
- Madelung, "Dynasties," 228
- Madelung, "Banu Saj"
- Bosworth, C.E. The History of the Saffarids of Sistan and the Maliks of Nimruz (247/861 to 949/1542-3). Costa Mesa, California: Mazda Publishers, 1994.
- Madelung, Wilfred. "Banu Saj." Encyclopaedia Iranica. Ed. Ehsan Yarshater. Columbia University. Retrieved 17 August 2011.
- Madelung, Wilferd. "Minor Dynasties of Northern Iran." The Cambridge History of Iran, Volume 4: The Period From the Arab Invasion to the Saljuqs. Ed. R. N. Frye. New York, New York: Cambridge University Press, 1975.