Narrated Anas bin Malik:

(The Caliph 'Uthman ordered Zaid bin Thabit, Said bin Al-As, 'Abdullah bin Az-Zubair and 'Abdur-Rahman bin Al-Harith bin Hisham to write the Quran in the form of a book (Mushafs) and said to them. "In case you disagree with Zaid bin Thabit (Al-Ansari) regarding any dialectic Arabic utterance of the Quran, then write it in the dialect of Quraish, for the Quran was revealed in this dialect." So they did it.

حَدَّثَنَا أَبُو الْيَمَانِ، حَدَّثَنَا شُعَيْبٌ، عَنِ الزُّهْرِيِّ، وَأَخْبَرَنِي أَنَسُ بْنُ مَالِكٍ، قَالَ فَأَمَرَ عُثْمَانُ زَيْدَ بْنَ ثَابِتٍ وَسَعِيدَ بْنَ الْعَاصِ وَعَبْدَ اللَّهِ بْنَ الزُّبَيْرِ وَعَبْدَ الرَّحْمَنِ بْنَ الْحَارِثِ بْنِ هِشَامٍ أَنْ يَنْسَخُوهَا، فِي الْمَصَاحِفِ وَقَالَ لَهُمْ إِذَا اخْتَلَفْتُمْ أَنْتُمْ وَزَيْدُ بْنُ ثَابِتٍ فِي عَرَبِيَّةٍ مِنْ عَرَبِيَّةِ الْقُرْآنِ فَاكْتُبُوهَا بِلِسَانِ قُرَيْشٍ، فَإِنَّ الْقُرْآنَ أُنْزِلَ بِلِسَانِهِمْ فَفَعَلُوا.