Complex sentence: Ubayd Allah abdicated the governor's mansion in Basra and took up shelter with Mas'ud ibn Amr al-Azdi of the Yemenite tribe Azd-who then supported the Umayyads against the rebellion of Abd Allah ibn al-Zubayr.
Split into simpler sentences: Ubayd Allah abdicated the governor's mansion in Basra and took up shelter with Mas'ud ibn Amr al-Azdi. The Azd were a Yemenite tribe who then supported the Umayyads against the rebellion of Abd Allah ibn al-Zubayr.