On the death of Yazdjurd, Uthman directed Abdullah bin 'Aamir the Governor General of Basra to undertake campaigns for the reconquest of Khurasan. Abdullah b 'Aamir took the field in person and marched at the head of a large force to Khurasan.
The vanguard of the Muslim force was led by Ahnaf b Qais. Crossing the Khurasan border he laid siege to two forts that served as the gates to Khurasan. The Persian garrisons there offered some resistance which was soon overcome, and the forts were captured by the Muslims. After garrisoning these forts, Ibn 'Aamir spread Muslim columns in various directions, and thus a multi pronged attack was launched on Khurasan. The strategy of the Muslims was that the Persians should not be allowed to combine their forces.
A Muslim column advanced to the town of Rustaq Zam and captured it by assault. Another column captured the town of Bakharz. A third column invested the town of Juban, and captured it after a short siege. Another column under Aswad b Kulsum advanced to Bayak. The Persians shut themselves in the city and closed the gates. The siege dragged on for some days with no tangible results. One night Aswad b Kulsum managed to enter the city through a drain. The Muslim army followed him. A severe hand to hand fight took place in the city. Aswad b Kulsum fell fighting. His brother Udham b Kulsum then took the standard and charged the enemy with violence. The Persians surrendered and the Muslims became the masters of Bayak. Thereafter the Muslims advanced to Tabisan which was captured after some show of resistance by the Persians.
Having conquered the region around Nishapur the Muslim force advanced to the main city of Nishapur. The city was divided into four sectors and each sector was under a Persian chief. These chiefs decided to defend the city. They shut themselves in the city and closed the gates. The Muslims invested the city. The siege dragged on for some days, and the Muslims intensified the blockade. In the meantime the Persian chiefs quarreled among themselves. One of the chiefs entered into negotiations with the Muslims. He offered to open one of the gates for the Muslim army to enter provided he was granted immunity. The Muslims accepted the offer. One night one of the gates of the city was opened whereby the Muslim army entered the city. The Persians were taken by surprise, and the Muslims became the masters of Nishapur. After consolidating their position at Nishapur the Muslims conquered other pockets around Nishapur. These included: Pusht, Ashband, Rukh, Zar, Khawaf, Osparain and Arghian.
Thereafter the Muslim force advanced to Abrshahr. The Persians chose to defend the city. The Persians shut themselves in the city and closed the gates. The Muslims besieged the town and the siege dragged on for more than a month. The Muslims succeeded in winning over one of the watchmen. One night he opened the gate and the Muslim army entered the city. The Persians taken by surprise surrendered, and agreed to pay an annual tribute. Thereafter a Muslim column was sent to Nish which fell to the Muslims after feeble resistance. Thereafter the Muslim column advanced to Nasaa which fell to the Muslims after some fighting. Thereafter the town of Abiur was captured. The Muslim force next advanced to Sarakhs. The city was besieged. After some days the chief entered into negotiations with the Muslims for peace. He wanted safety for one hundred persons. l he offer was accepted. In the list of one hundred persons that he submitted he forgot to include his own name. The city of Sarakhs surrendered and after granting immunity to one hundred persons the other male adult population of the city including the chief was put to death. The victor of Sarakhs was Abdullah b Khazam Salmi. The Muslims won immense booty here. Among the women taken captive was a daughter of the chief who was a great beauty. Ibn Khazam married her, after she was converted to Islam and was renamed Misa.
From Sarakhs a column was sent to Kaif and Bayna. Both the towns were captured.
By this time the Muslims had reconquerd a greater part of Khurasan. That weakened the will to resist in the case of the chiefs of the other parts of Khurasan. Before the Muslim forces could advance to Tus, the chief of Tus, Kanaztuk waited on Ibn 'Aamir, and offered his submission on the payment of tribute. The offer was accepted. Ibn Aamir sent a column to overpower Herat. Before this force could reach Herat, the chief of Herat waited on Abdullah b 'Aamir, and offered submission on the usual terms with regard to Herat, Badghis, and Bushang. This offer was also accepted. When the Muslim column reached Herat there was no fight. The two towns of Taghun and Yaghun in Herat, however chose to fight. They were captured after some fighting.
Thereafter the Muslim force advanced to Merv. The chief of Merv Shah Jahan by name waited on Ibn A'amir, and offered his submission. Peace was made on the people of Merv agreeing to pay an annual tribute. in the peace treaty it was
also stipulated that some lands would be allotted to the Muslims for their settlement in Khurasan. A town in the neighborhood of Merv, Sang by name which was the residence of some military men refused to surrender. The Muslims advanced against the town and conquest it by force.
After the treaty of Merv the whole of Khurasan had become subject to the suzerainty of the Muslims. The remoter part of Khurasan known as Taghiristan alone remained independent. Ibn 'Aamir commissioned Ahnaf b Qais to undertake campaigns in Taghiristan. In its advance in Taghiristan the Muslim force had its first encounter with the Persian force at Najirid. The Persians were defeated and peace was made on their undertaking to pay an annual tribute. Ahnaf stayed at Najirid for some time and then advanced to Marvul Roz. Here resistance was offered to the Muslim force, but it proved to be of no avail. The chief sued for peace, which was made on his agreeing to undertake the payment of an annual tribute. Thereafter the Muslim column advanced to Bugh which was captured after some fight. At some distance from Bugh the Persians rallied again and put up stiff resistance. They were however defeated. Many were taken captive who were killed. The rest of them fled to Jurjan. Thc Muslims pursued them to Jurjan which town was occupied after some fight. Thereafter the Muslim force advanced to Balkh. There was not much of fighting at Balkh and the city surrendered and agreed to pay an annual tribute. With the fall of Balkh, the Muslims became the masters of the whole of Khurasan. The campaigns in Khurasan lasted for some three years from 651 to 654 C.E.