Usool At-tafseer by Shu‘bah ibn al-Hajjaaj, Sufyaan ibn ‘Uyaynah and it was translated by Dr. M. Abdul Haq Ansari

The Qur’aan continued to be read according to the seven forms until midway through Caliph ‘Uthmaan’s rule, when some confusion arose in other outlying provinces concerning the Qur’aan’s recitation. Some Arabic tribes had begun to boast about the superiority of their readings and a rivalry began to develop. At the same time, some new Muslims also began mixing the various forms out of ignorance. Caliph ‘Uthmaan decided to make official copies of the Qur’aan according to the dialect of Quraysh and send them along with Qur’aanic reciters to the major centers of Islaam. This decision was approved by all of the sahaabah, and all unofficial copies of the Qur’aan were destroyed. Following the distribution of the official copies, all the other dialects were dropped and the Qur’aan began to be read in only one dialect. Thus, the Qur’aan which is available throughout the world today is written and recited only according to the dialect of the Quraysh.29

The discontinuance of the other six forms does not in any way represent a loss of any part of the Qur’aan. The sahaabah were given the option by the Prophet (ﷺ) to recite the Qur’aan in any of the seven dialects they wished because the meaning was the same and the variations were synonymous; and it is they who unanimously decided to discontinue the use of the other six. Such a decision could not have been unanimously approved if it in any way entailed the loss of even the smallest part of the Qur’aan. Thus, the Qur’aan according to the Qurayshee dialect is, without doubt, a perfect and complete compilation of Allaah’s revealed word to the last of His prophets and messengers, Muhammad (ﷺ).