Musnad Ahmad 5:201

'Abd al-Rahman narrated to us, Zuhayr narrated to us, from 'Abd Allah—meaning Ibn Muhammad ibn 'Aqil—from Muhammad ibn 'Ali, that he heard 'Ali ibn Abi Talib saying: The Messenger of Allah (peace and blessings of Allah be upon him) said: "I have been given what no one among the prophets was given." We said: "O Messenger of Allah, what is it?" He said: "I have been granted victory through awe, I have been given the keys of the earth, I have been named Ahmad, the earth has been made a means of purification for me, and my nation has been made the best of nations."