In May 633 AD, the Muslim Arabs, under Khalid ibn al-Walid, attacked the fortressed city, whose Lakhmid defenders utilized projectiles against the Muslims. The fight was brief and the citizens of the city quickly surrendered and brought gifts to Khalid ibn al-Walid. In the aftermath, five castles in the city, which were beautifully adorned, fell into the hands of the Muslims and the inhabitants of the city agreed to surrender and pay tribute. The inhabitants also agreed to act as spies against the Sassanians, just as the inhabitants of Ullais had.
^ abConflict and Cooperation: Zoroastrian Subalterns and Muslim Elites in Medieval Iranian Society By Jamsheed Kairshasp Choksy, pg. 14
^Muhammad's People: An Anthology of Muslim Civilization By Eric Schroeder,pg.160
^After the battle of Ullais (15,000 Muslim army) in which around 2000 muslims died the army strength must be ~10,000-15,000 along with reinforcement or possible new recruits from Misna ibn Haris's tribe of Bani Bakr in Iraq.