 Muhammad also had an ally in his nephew Muhammad b. Tahir, who was the governor of most of the eastern provinces, although at the time the latter was largely preoccupied with the rebellion of Hasan b. Zayd in Tabaristan.In order to augment the ranks of his soldiers, Muhammad instituted a draft in Baghdad and called on for volunteers to serve al-Musta'in.A group of Khorasani pilgrims en route to Mecca at the time the war began were asked to stay and fight.