On the Persian front, Muthana ibn Haritha, who took over the supreme command from Khalid ibn al-Walid after the latters departure to Syria, died soon after the battle of Buwayb in 635. The new commander-in-chief was Sad ibn Abi Waqqas [RA], one of the Prophet [peace and blessings be upon him]s Companion and an experienced soldier who had taken part in the famous battles of Badr  and Uhud .
Meanwhile the Persians made a final effort to overcome their internal differences and gathered a large and well equipped army under Rustam. The two armies confronted each other at Qadisiyah, about twenty miles south-west of Hira and near the future of Najaf (637J,and the Muslims inflicted a severe defeat on the Persians. Rustam was killed and the retreating army left behind the imperial standard, the sacred palladium of the mighty Sasanid Empire,and the whole Iraq fell under Muslim control
The surrender of Jerusalem
Jerusalem was besieged and its Greek Patriarch, the honey tongue Sophronius, who had been appointed by Emperor Heraclius, soon surrendered so that Umar ibn Khattab [RA], who was on a visit to the military camp of Jabiya [some twenty miles north of the sea of Galilee] after the battle of Yarmuk. came 111 person to accept the submission.
The terms of surrender were drawn up and the Caliph set out for the holy city Christians were granted protection and allowed to follow their religion in return for payment of a poll tax (Jizyah] which was less heavy than that which the Byzantines had imposed upon them. Umar [RA]visited the once occupied temple of Solomon and ordered that a mosque be built there which later came to bear his name.
This article was culled from the publications of Deen Communication Limited