"...So, this area that we are in, Afghanistan, was subject to Persian Magian rule...Badakhshan, the northern provinces, Juzjan, etc. all the way to Takhar and Herat. Khurasan was part of the Persian empire, and Bukhara and Samarqand were all part of the Persian empire. How did 'Uthman conquer it?
Do you not see me guided after I was misguided * And I became a soldier in the army of Ibn 'Affan?
So, all of these areas were conquered in the era of 'Uthman, and 'Abd ar-Rahman bin Samurah conquered Kabul during the era of either 'Umar or 'Uthman. In the 'Sunan' of Abu Dawud, it says: "'Abd ar-Rahman bin Samurah narrated to us in Kabul." So, 'Abd ar-Rahman bin Samurah conquered Kabul during the era of 'Umar or 'Uthman, may Allah be Pleased with them both.
None of the populations that were conquered by the Muslims ever rebelled or resisted them except the people of Afghanistan. The people of Afghanistan are very stubborn, and it is not an easy task to make them submit. So, the Muslims conquered it during the era of 'Umar, and this was followed by a rebellion from some of the tribes and the expulsion of the Muslims, and the Muslims had to return later on and conquer Afghanistan a second time.
If the Afghans become convinced of an idea or belief, they are known to cling to it very tightly and spread it. This is why they carried the religion of Buddhism and the people of Afghanistan adopted it. There was no way to change them - Buddhism, that was it, and this is why there is a huge statue of Buddha still standing in Bamyan today.* They are the ones who spread Buddhism in the region - to Pakistan and India. The Afghans are the ones who spread it...some tribes became convinced of this belief and began spreading Buddhism.
Islam then came, they became convinced of Islam, and they spread it throughout the region. So, most of these areas adopted Islam through them, and Mahmud al-Ghaznawi invaded India seven times. He entered it and demolished their statue, Shamnama, and after this, the Afghan people adopted the Hanafi madhhab..."
[*] Obviously, that changed in March of 2001
['Fi Dhilal Surat at-Tawbah'; p. 141-142]
(SHEIKH 'ABDULLAH YUSUF 'AZZAM (ASY-SYAHID, INSYAALLAH)