This hadith has been transmitted on the authority of Shu'ba with the same chain of transmitters, and he said:"An Abyssinian slave."
وَحَدَّثَنَاهُ ابْنُ بَشَّارٍ، حَدَّثَنَا مُحَمَّدُ بْنُ جَعْفَرٍ، وَعَبْدُ الرَّحْمَنِ بْنُ مَهْدِيٍّ، عَنْ شُعْبَةَ، بِهَذَا الإِسْنَادِ وَقَالَ عَبْدًا حَبَشِيًّا .
Muslim
The Book on Government • Hadith 57