Contrary to the assertions of the later Arab 'historians', the Arabic among the different tribes of the Peninsula, due mainly to their geographical distribution, was markedly different from each other. It did not become a 'monolithic' language until after the Quran was made the language par excellence for all of Muhammadan Muslims.
The following statement, as well as other recorded reports, prove the point-
Sahih Al-Bukhari HadithHadith 4.709Narrated byAnas
Uthman called Zaid bin Thabit, Abdullah bin Az-Zubair, Said 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. (Said bin Thabit was an Ansari and not from Quraish ).
North-east Arabian dialects:Najd, in particular those of the large tribes 'Aniza and Shammar.
South-west Arabian dialects: Yemen, Hadramaut and Aden
West Arabian dialects: Hijaz and the Tihama
The urban centres of Mecca and Medina had their own dialects also.
In fact, the Hymiarites and the Yamanis in particular had their different writings beside that of their dialect vis a vis the Meccans. That is why UthmanINSISTED on the dialect of the Quraysh.
Even today, the spoken dialects of Arabic are much greater than in the days of Muhammad since they encompass those of the subjugated and Arabised peoples of North Africa, Syria, Iraq, Jordan, Lebanon, Israel, Palestinian territories to name a few.