Abbas 1 was the son of the caliph al-Ma'mun 1 and nephew of the caliph al-Mu`tasim 1 (Abu Ishaq): Chron. 1234, §§213, 215, 216, 218, 223 (II, pp. 24, 27, 28, 29, 35). Unnamed son of the caliph al-Ma'mun 1; in c. 830 he accompanied Manuel 1 on an expedition against the Romans, when Manuel instead returned to Constantinople, instructing Abbas to return to his father: Theoph. Cont. III 26 (p. 120), Scyl., p. 71. He was sent to accompany Manuel 1 on a campaign against the Romans; during the campaign Manuel left to return to the Romans, but he gave presents to the son of the caliph, which ensured that the Arabs remained well disposed towards him: Genesius III 17. According to the Syriac tradition, after the departure of Manuel, al-Ma'mun 1 prepared to invade the Byzantine empire accompanied by his son Abbas and his brother Abu Ishaq (al-Mu`tasim 1): Chron. 1234, §213 (II, p. 24). In the year 1144 Sel. (AD 833) Abbas and Abu Ishaq (al-Mu`tasim 1) led the vanguard of al-Ma'mun 1's troops on an invasion into Byzantine territory: Chron. 1234, §215 (II, p. 27). After the death of al-Ma'mun 1 on 23 Tammuz, AH 218 (23 July 833), the succession was disputed between Abbas and Abu Ishaq, until Abbas gave way in favour of his uncle: Chron. 1234, §216 (II, p. 28), §218 (II, p. 29).

Later he was reported to be planning a rebellion in Baghdad, not more than a year or so before the death of Abu Ishaq (which was in 842): Chron. 1234, §223 (II, p. 35). Son of the caliph Mamun (al-Ma'mun 1), whom he accompanied on the expedition into Cilicia during which Mamun died: Bar Hebr., p. 133. Brother of the caliph al-Mu`tasim 1, he conspired to kill his brother when the latter was engaged in the destruction of Amorion (therefore in 838); the plot was disclosed and `Abbas died of thirst at Mabbugh while being taken back in chains: Bar Hebr., p. 138.

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