It was narrated Muhammad bin Ali al-Akbar that he heard his father Ali bin Abi Talib (رضي الله عنه) say: The Messenger of Allah (ﷺ) said: `I have been given four thing that which was not given to any of the other Prophets.” I have been given the keys of the Earth, I have been named Ahmad, the dust has been made a means of purification for me and my ummah has been made the best of nations.`
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا أَبُو سَعِيدٍ، حَدَّثَنَا سَعِيدُ بْنُ سَلَمَةَ بْنِ أَبِي الْحُسَامِ، حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مُحَمَّدِ بْنِ عَقِيلٍ، عَنْ مُحَمَّدِ بْنِ عَلِيٍّ الْأَكْبَرِ، أَنَّهُ سَمِعَ أَبَاهُ، عَلِيَّ بْنَ أَبِي طَالِبٍ رَضِيَ اللَّهُ عَنْهُ يَقُولُ قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أُعْطِيتُ أَرْبَعًا لَمْ يُعْطَهُنَّ أَحَدٌ مِنْ أَنْبِيَاءِ اللَّهِ أُعْطِيتُ مَفَاتِيحَ الْأَرْضِ وَسُمِّيتُ أَحْمَدَ وَجُعِلَ التُّرَابُ لِي طَهُورًا وَجُعِلَتْ أُمَّتِي خَيْرَ الْأُمَمِ.
sunnah.com