Collection of the Quran at the time of Uthman
At the time of Uthman, people in the different regions of the Islamic
state started disputing over the different recitations of the Quran.
This difference was not due to a change in the Quran, but due to the
different Ahruf/accents that the Quran was revealed in. So, the
students of ibn Mas'ood might differ with the students of Ubayy for
example. This in fact was not something new. Even during the time of
the Prophet, we know the story of Umar disputing the recitation of
another companion. When both complained to the Prophet, the Prophet
endorsed both recitations. At the time of Uthman however, lots of
people were entering the new religion, and some of them did not
appreciate the different modes of recitation. There is one narration
in Sahih al-Bukhari that Hudhaifa came to Uthman from Armenia
explaining the state of the people over there and how they differed on
recitation to a point that there were accusing each other of heresy.
Then Uthman knew that if he didn't do something the Ummah was going to
disunite on this. So, he gathered a panel of few companions like Zaid
bin Thabit (the scribe of the Prophet), Abdullah bin az-Zubair and
others. The mission was to access the scrolls that Abu Bakr collected
of the Quran, make several copies of it, and organize the Surahs into
a book (Mushaf). Uthman was well aware of the different accents of
the Quran, and he tried his best to include them in the new copies
whenever possible. For example, in surat al-Fatiha, Malik and Maalik
are two valid recitations. So, by not writing the Alif, it was
possible that both recitations were preserved. Whenver it was not
possible, Uthman ordered that the accent of Quraish would be followed
since it was the accent of the Prophet. Yet, sometimes the different
copies were made to accomodate the difference. So, the copies that
Uthman sent to the different regions were not exactly the same because
one of them might have one recitation and the other had another
recitation. As to ibn Ma'ood, it's recorded that he complained to the
fact that he was not selected to be part of the panel. But the
scholars have answered that ibn Masud was in Kufa so he was far and
this was an urgent manner. In addition, Zaid bin Thabit was chosen
because he was the scribe of the Prophet and he was also the scribe
who wrote the Quran of Abu Bakr. Moreover, his tongue was Quraishi
whereas the tongue of ibn Masud was Hudhali, and it's mentioned above
how Uthman preferred the tongue of Quraish.