 When 'Abdallah died in 844, the Caliph al-Wathiq originally appointed another Tahirid, Ishaq ibn Ibrahim ibn Mus'ab, as his successor in Khurasan, but then reversed this decision and confirmed Tahir as governor.Little is known about Tahir's reign, although there was unrest in some of the outlying provinces.Sistan, for example, was lost to the Tahirids when the 'ayyar leader Salih ibn al-Nadr drove out Tahir's governor and took power there himself.