Allah has commanded you to recite to your people the Quran in one dialect. Upon this he said: I ask from Allah pardon and forgiveness. My people are not capable of doing it. He then came for the second time and said: Allah has commanded you that you should recite the Quran to your people in two dialects. Upon this he (the Holy prophet) again said: I seek pardon and forgiveness from Allah, my people would not be able to do so. He (Gabriel) came for the third time and said: Allah has commanded you to recite the Quran to your people in three dialects. Upon this he said: I ask pardon and forgiveness from Allah. My people would not be able to do it. He then came to him for the fourth time and said: Allah has commanded you to recite the Quran to your people in seven dialects, and in whichever dialect they would recite, they would be right.
Sahih Muslim Book 6, Hadith 334