Khazars and King Convert to Islam in 965 CE

E.J. Brill's First Encyclopedia of Islam, 1913-1936

"According to Ibn al-Athir, the Khazars and later their king were converted to Islam in 354 AH (965 CE) when they had to defend themselves with the help of the Khwarizmis against an attack by a Turkic people; this story, which we find as early as Ibn Miskawaih is undoubtedly taken from the lost work of Thabit b. Sinan and we must agree with Fr. Westburg in referring it to the known campaign of Swyatoslaw. What al-Mukaddasi tells us about the adoption of Islam as a result of the campaigns of al-Mamun, does not refer, as Marquart supposes, to the Caliph, but, as a comparison with al-Mukaddasi shows, to the ruler of Gurgandi (Arabic Djurdjaniya) and afterwards of all Khwarizm, Abu 'l-'Abbas Mamun b.Muhammad."