IBAS (Hiba). - Bishop of Edessa, d. 28 Oct. 457. He was Edessa (v.) under Bishop Rabbula, alongside whom he attended the Council of Ephesus, but siding with the Antiochenes. When Rabbula condemned the works of Theodore of Mopsuestia, Ibas was displeased. After peace was made between the Antiochenes and St. Cyril of Alexandria (433), Ibas was expelled from Edessa by his bishop, and it was probably at this time that he wrote his letter to Mārī, bishop of Rēwardašīr in Persia.
He also propagated the works of Theodore of Mopsuestia through Armenian translations, which led Rabbula and later Proclus of Constantinople to warn the Armenians against Nestorian doctrines. In 435, Ibas was elected bishop of Edessa. Already in 445 he was accused of Nestorianism before the patriarch of Antioch, but he did not appear. Accused again in 448, and by order of Theodosius II, Ibas presented himself before the tribunals of Tyre and Beirut, where he denied being a Nestorian, but his accusers produced his letter. Ibas was able to return to Edessa; however, in 449 Theodosius II had him appear again at the "Robber Synod" of Ephesus, instigated by the Monophysites, where he was deposed. But at the Council of Chalcedon (451), at which he was present, he was rehabilitated after the reading of his letter, though with the condemnation of Nestorius. Nevertheless, at the Council of Constantinople in 553, one of the Three Chapters condemned was precisely the letter of Ibas.
This letter, undoubtedly written in Syriac, is preserved only in Greek (E. Schwartz, Acta Conc., II, Berlin, 1, 3, p. XXIII ff.). It has a certain Nestorian flavor, accusing the doctrine of St. Cyril of Apollinarianism, distinguishing between the Word and His temple born of Mary, and seemingly ignoring the communication of idioms in Christ.