Sahih Bukhari Volume 4, Book 56, Hadith 2970

حَدَّثَنَا الْفَضْلُ بْنُ سَهْلٍ، حَدَّثَنَا حُسَيْنُ بْنُ مُحَمَّدٍ، حَدَّثَنَا جَرِيرُ بْنُ حَازِمٍ، عَنْ مُحَمَّدٍ، عَنْ أَنَسِ بْنِ مَالِكٍ ـ رضى الله عنه ـ قَالَ فَزِعَ النَّاسُ فَرَكِبَ رَسُولُ اللَّهِ صلى الله عليه وسلم فَرَسًا لأَبِي طَلْحَةَ بَطِيئًا، ثُمَّ خَرَجَ يَرْكُضُ وَحْدَهُ، فَرَكِبَ النَّاسُ يَرْكُضُونَ خَلْفَهُ، فَقَالَ ‏"‏ لَمْ تُرَاعُوا، إِنَّهُ لَبَحْرٌ ‏"‏‏.‏ فَمَا سُبِقَ بَعْدَ ذَلِكَ الْيَوْمِ‏

Narrated By Anas bin Malik : Once the people got frightened, so Allah's Apostle rode a slow horse belonging to Abu Talha, and he set out all alone, making the horse gallop. Then the people rode, making their horses gallop after him. On his return he said, "Don't be afraid (there is nothing to be afraid of) (and I have found) this horse a very fast one." That horse was never excelled in running hence forward.