Ustadh Sis, also spelled: Ustad Sis, or Ostad Sis, Persian: استاذ سیس Persian heresiarch, and anti-Arab rebel leader.
His name in Persian means Master of Sis, he claimed he is a prophet of God among in the eastern fringe of Khorasan in the mid 8th century, and managed to gain followers among the villagers in that area, many of whom were followers of Bihafarid, whom the Abbasid commander, Abu Muslim militarily crushed. His initial base was the mountainous region of Badghis, and later occupied Herat, Sistan and marched towards Merv. He initially defeated an Abbasid army under the command of al-Ajtham of Merv, but was himself defeated in a bloody battle against an army led by al-Mahdi, the son of the Caliph al-Mansur (and a future Caliph himself). Sources say that 70,000 of Ustadh Sis's followers were killed in the battle, and 14,000 were taken captive. Ustadh Sis managed to flee to the mountains, but the general Khazim ibn Khuzaimah al-Tamimi followed him and was able to capture him. Ustadh Sis was sent in chains to al-Mansur, who ordered his execution. al-Mahdi gave amnesty to 30,000 captives.
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