Language:
كتاب الجهاد والسير
56  
Fighting for the Cause of Allah (Jihaad)
(46)
Chapter: To name a horse and a donkey
(46)
باب اسْمِ الْفَرَسِ وَالْحِمَارِ
Sahih al-Bukhari 2857

Narrated Anas bin Malik:

Once there was a feeling of fright in Medina, so the Prophet (ﷺ) borrowed a horse belonging to us called Mandub (and he rode away on it). (When the Prophet (ﷺ) returned) he said, "I have not seen anything of fright and I found it (i.e. this horse) very fast."

حَدَّثَنَا مُحَمَّدُ بْنُ بَشَّارٍ، حَدَّثَنَا غُنْدَرٌ، حَدَّثَنَا شُعْبَةُ، سَمِعْتُ قَتَادَةَ، عَنْ أَنَسِ بْنِ مَالِكٍ ـ رضى الله عنه ـ قَالَ كَانَ فَزَعٌ بِالْمَدِينَةِ، فَاسْتَعَارَ النَّبِيُّ صلى الله عليه وسلم فَرَسًا لَنَا يُقَالُ لَهُ مَنْدُوبٌ‏.‏ فَقَالَ ‏ "‏ مَا رَأَيْنَا مِنْ فَزَعٍ، وَإِنْ وَجَدْنَاهُ لَبَحْرًا ‏"‏‏.‏
Reference : Sahih al-Bukhari 2857
In-book reference : Book 56, Hadith 73
USC-MSA web (English) reference : Vol. 4, Book 52, Hadith 109
  (deprecated numbering scheme)