Jabalah Ibn Al-Aiham (Arabic: جبلة ابن الأيهم) was the last ruler of the Ghassanid state in Syria and Jordan in the seventh century AD. He commanded a Christian Arab army in the Battle of Yarmouk in 636. After the Muslim conquest of the Levant he converted to Islam around the year 638. He later returned to Christianity and lived in Anatolia until he died in the year 645.
There are different opinions why Jabalah and his followers didn't convert to Islam. All the opinions go along the general idea that the Ghassanids were not interested yet in giving up their status as the lords and nobility of Syria below the famous story of Jabalah return to the Byzantines land.
Jabalah Ibn-Al-Aiham sided with the Ansar (Azdi Muslims from Medina) saying, "You are our brethren and the sons of our fathers" and professed Islam. After the arrival of 'Umar ibn-al-Khattab in Syria, in the year 17 (638 AD), Jabalah was conducting a pilgrimage in Mecca. During his tawaf around the kaaba a poor man mistakenly stepped on his robe, making Jabalah almost trip over. This angered Jabalah so much that he hit the man in the eye, after which the man went to the Caliph 'Umar bin Khattab, who then requested that Jabalah be summoned to trial. After displaying the facts of the case, 'Umar ordered that Jabalah be hit by the poor man on the eye in the same manner by which the man himself was hit, but Jabala resisted this saying "Is his eye like mine?" upon which the Caliph 'Umar responded that "Islam has made you both equal." Jabalah requested that the Caliph carry out the sentence the next morning, and he fled to his village during the night. He then apostatized and went to the land of the Greeks (the Byzantines). This Jabalah was the king of Ghassan and the successor of al-Harith ibn-abi-Shimr.