Sayyiduna Ali bin Abi Talib (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "I have been given what was not given to any prophet before me." We said: O Messenger of Allah! What is it? He (peace and blessings be upon him) said: "I have been helped with awe, I have been given the keys of the earth, I have been named Ahmad, the soil has been made pure for me, and my Ummah has been made the best of nations."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1024