After the conquest of Jalaula, a Muslim force under Qaqaa marched in pursuit of the Persians.
The Persian army that escaped from Jalaula took its position at Khaniqeen fifteen miles from Jalaula on the road to Iran. The Persian force at Khaniqeen was commanded by General Mihran. His deputy was Feerzan. The force at Khaniqeen was joined by some reinforcements from Hulwan.
When Qaqaa arrived at Khaniqeen he deployed for battle. Mihran and Feerzan also arrayed their army for battle on the plain outside Khaniqeen.
The battle began with a duel between Qaqaa and Mihran. In this duel Mihran was killed. With the death of Mihran, the Muslims launched the attack with considerable violence. The Persians put up a defence but it did not last long. Feerzan and the force he commanded found safety in flight.
With the withdrawal of the Persian army Khaniqeen was captured by the Muslims. A good deal of booty was captured by the Muslims which was distributed after setting aside the state share of one fifth. In this battle a large number of Persian women was captured by the Muslims. These were also distributed among the Muslim soldiers.
When Yazdjurd the Persian emperor came to know of the defeat of the Persians at Khaniqeen he left the defence of Hulwan to a general named Khusro Shanum, and himself fled to Qum.
From Khaniqeen Qaqaa marched to Hulwan. At Hulwa the Persian forces under Khusro Shanum offered resistance. On a cold January day in the year 638 AD, the Muslim and the Persian forces clashed on the battle-field. The Muslims fought with great vigour and violence The Persians put up a stiff resistance but they felt that the Muslims were devils and jinns and they could be no match for them. The Persians lost heart as well as the battle. Khusro Shanum and his forces found safety in flight.
With the withdrawal of the Persian forces the citizens of Hulwan formally submitted to Muslim rule and agreed to pay Jizya. Hulwan was a large city and Qaqaa stayed there to restore law and order and administer its affairs.
A considerable booty was captured by the Muslims. It was distributed in the usual way and the one fifth state share was sent to Ctesiphon and Madina.
Qaqaa sent a report of the victory of Hulwan to Saad. He chose to stay at Hulwan pending receipt of further orders. Qaqaa suggested that he should be allowed to continue his advance to North Persia in the pursuit of the defeated Persian army. He also desired that if such advance was to be made further reinforcements should be sent.
Sa'ad transmitted the report to Umar at Madina. He recommended that the Muslim forces should be allowed to march further inland in Persia.
Umar thanked God for the victory of the Muslims at Hulwan. He took counsel with the Companions whether the Muslim forces should continue their advance in the heart of Persia. Umar was of the opinion, and this view was endorsed by the Muslims in Madina, that there should be halt to further advance.
Umar accordingly wrote to Sa'ad bin Abi Waqq as that there should be no further advance. He wrote:
"I wish that between the Suwad and the Persian hills there were a wall which would prevent them from getting to us, and prevent us from getting to them. The fertile Suwad is sufftcient for us; and I prefer the safety of the Muslims to the spoils of war."
In view of this policy of no further advance Qaqaa was withdrawn from Hulwan to rejoin the main force at Ctesiphon. Qaqaa left Qubas b. Abdullah as the Commander of the Muslim garrison at Hulwan. The garrison was to guard the frontiers of Islam. Jareer b. Abdullah withdrew from Jalaula leaving a small Muslim force there.
By February 638 there was a lull in fighting on the Persian front. The Suwad, the Tigris valley, and the Euphrates valley were now under the complete control of the Muslims. The Persians had withdrawn to Persia proper. It appeared as if this was going to be the dividing line between the Arabs and the Persians.