Brief accounts of Ishoʿ bar Nun's patriarchate are given in the Ecclesiastical Chronicle of the Jacobite writer Bar Hebraeus (floruit 1280) and in the ecclesiastical histories of the Nestorian writers Mari (twelfth-century), ʿAmr (fourteenth-century) and Sliba (fourteenth-century).
Modern assessments of Ishoʿ bar Nun's reign can be found in Jean-Maurice Fiey's Chrétiens syriaques sous les Abbassides and David Wilmshurst's The Martyred Church.
He had resided for thirty-eight years in the monastery of Deir Saʿid near Mosul, and was very well versed in doctrine.
He wrote a confutation of the writings of the catholicus Timothy and criticised everything he did, calling him Tolemathy, that is, injurious to God.
'[2] Ishoʿ bar Nun was widely respected as a theologian and a canonist, and was a prolific author in a number of genres.