Muhammad bin ‘Umar (Imaam Waaqidi) (rahimahullah) says that he heard Imaam Maalik (rahimahullah) mention the following:

When Al-Mansoor (the Muslim ruler) performed Haj, he summoned me. I thus answered his summons and went to him. After entering into his presence, we held a conversation during which he asked me questions and I answered him.

Al-Mansoor then said to me, “I have decided to instruct for copies to be made of your kitaabs (i.e. the kitaabs of Imaam Maalik (rahimahullah) that formed his compilation of Hadith known as Al-Muwatta) after which I will send one copy to each city of the Muslims. I will command them to practice on what is in your kitaab and abandon all other knowledge which has reached them. I wish to do this because I feel that the basis of knowledge is only the narrations and knowledge of the people of Madinah Munawwarah.”