Sahih Muslim 1298 a
Umm al-Husain (Allah be pleased with her) reported:
I performed Hajj along with Allah's Messenger (ﷺ) on the occasion of the Farewell Pilgrimage and saw him when he flung pebbles at Jamrat al-'Aqaba and returned while he was riding the camel, and Bilal and Usama were with him. One of them was leading his camel, while the other was raising his cloth over the head of Allah's Messenger (ﷺ) to protect him from the sun. She (further) said: Allah's Messenger (ﷺ) said so many things, and I heard him saying: If a slave having some limb of his missing and having dark complexion is appointed to govern you according to the Book of Allah the Exalted. listen to him and obey him.
وَحَدَّثَنِي سَلَمَةُ بْنُ شَبِيبٍ، حَدَّثَنَا الْحَسَنُ بْنُ أَعْيَنَ، حَدَّثَنَا مَعْقِلٌ، عَنْ زَيْدِ بْنِ أَبِي، أُنَيْسَةَ عَنْ يَحْيَى بْنِ حُصَيْنٍ، عَنْ جَدَّتِهِ أُمِّ الْحُصَيْنِ، قَالَ سَمِعْتُهَا تَقُولُ، حَجَجْتُ مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم حَجَّةَ الْوَدَاعِ فَرَأَيْتُهُ حِينَ رَمَى جَمْرَةَ الْعَقَبَةِ وَانْصَرَفَ وَهُوَ عَلَى رَاحِلَتِهِ وَمَعَهُ بِلاَلٌ وَأُسَامَةُ أَحَدُهُمَا يَقُودُ بِهِ رَاحِلَتَهُ وَالآخَرُ رَافِعٌ ثَوْبَهُ عَلَى رَأْسِ رَسُولِ اللَّهِ صلى الله عليه وسلم مِنَ الشَّمْسِ - قَالَتْ - فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم قَوْلاً كَثِيرًا ثُمَّ سَمِعْتُهُ يَقُولُ ‏
"‏ إِنْ أُمِّرَ عَلَيْكُمْ عَبْدٌ مُجَدَّعٌ - حَسِبْتُهَا قَالَتْ - أَسْوَدُ يَقُودُكُمْ بِكِتَابِ اللَّهِ تَعَالَى فَاسْمَعُوا لَهُ وَأَطِيعُوا ‏"‏ ‏.‏