From Sahih Bukhari (Hadith 3506):
Narrated Anas:`Uthman called Zaid bin Thabit, `Abdullah bin Az-Zubair, Sa`id bin Al-`As and `AbdurRahman bin Al-Harith bin Hisham, and then they wrote the manuscripts of the Holy Qur'an in the form of book in several copies. `Uthman said to the three Quraishi persons, "If you differ with Zaid bin Thabit on any point of the Qur'an, then write it in the language of Quraish, as the Qur'an was revealed in their language." So they acted accordingly. (Zaid bin Thabit was an Ansari and not from Quraish)
Reference: Bukhari 3506