 Complete the following phrase:  In 1132 Ayyub was in the service of Imad ad-Din Zengi. He participated in a battle against the Seljuk Sultan near Tikrit and saved Zengis life when he assisted his retreat across the Tigris. In 1136, Shirkuh killed a Christian with whom he was quarrelling in Tikrit, and the brothers were exiled Ayyubs son Yusuf, later known as Saladin, was supposedly born the night they left. Zengi later appointed Ayyub governor of Baalbek, and when the town was besieged in 1146 by Muin ad-Din Unur, the atabeg of the Burid emir of Damascus, Ayyub surrendered Baalbek and retired to Damascus. Shirkuh, meanwhile, entered the service of Zengis son Nur ad-Din Zengi, who had designs on Damascus; when the Second Crusade 