Sahih al-Bukhari 4054
Narrated Sa`d bin Abi Waqqas:
I saw Allah's Messenger (ﷺ) on the day of the battle of Uhud accompanied by two men fighting on his 
behalf. They were dressed in white and were fighting as bravely as possible. I had never seen them 
before, nor did I see them later on.
حَدَّثَنَا عَبْدُ الْعَزِيزِ بْنُ عَبْدِ اللَّهِ، حَدَّثَنَا إِبْرَاهِيمُ بْنُ سَعْدٍ، عَنْ أَبِيهِ، عَنْ جَدِّهِ، عَنْ سَعْدِ بْنِ أَبِي وَقَّاصٍ ـ رضى الله عنه ـ قَالَ رَأَيْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَوْمَ أُحُدٍ، وَمَعَهُ رَجُلاَنِ يُقَاتِلاَنِ عَنْهُ، عَلَيْهِمَا ثِيَابٌ بِيضٌ، كَأَشَدِّ الْقِتَالِ، مَا رَأَيْتُهُمَا قَبْلُ وَلاَ بَعْدُ‏.‏