Language:
كتاب الجهاد والسير
56  
Fighting for the Cause of Allah (Jihaad)
(82)
Chapter: The straps for suspending sword and the hanging of the sword by the neck
(82)
باب الْحَمَائِلِ وَتَعْلِيقِ السَّيْفِ بِالْعُنُقِ
Sahih al-Bukhari 2908

Narrated Anas:

The 'Prophet was the best and the bravest amongst the people. Once the people of Medina got terrified at night, so they went in the direction of the noise (that terrified them). The Prophet (ﷺ) met them (on his way back) after he had found out the truth. He was riding an unsaddled horse belonging to Abu Talha and a sword was hanging by his neck, and he was saying, "Don't be afraid! Don't be afraid!" He further said, "I found it (i.e. the horse) very fast," or said, "This horse is very fast." (Qastala-ni)

حَدَّثَنَا سُلَيْمَانُ بْنُ حَرْبٍ، حَدَّثَنَا حَمَّادُ بْنُ زَيْدٍ، عَنْ ثَابِتٍ، عَنْ أَنَسٍ ـ رضى الله عنه ـ قَالَ كَانَ النَّبِيُّ صلى الله عليه وسلم أَحْسَنَ النَّاسِ وَأَشْجَعَ النَّاسِ، وَلَقَدْ فَزِعَ أَهْلُ الْمَدِينَةِ لَيْلَةً فَخَرَجُوا نَحْوَ الصَّوْتِ فَاسْتَقْبَلَهُمُ النَّبِيُّ صلى الله عليه وسلم وَقَدِ اسْتَبْرَأَ الْخَبَرَ، وَهْوَ عَلَى فَرَسٍ لأَبِي طَلْحَةَ عُرْىٍ وَفِي عُنُقِهِ السَّيْفُ وَهْوَ يَقُولُ ‏"‏ لَمْ تُرَاعُوا لَمْ تُرَاعُوا ‏"‏‏.‏ ثُمَّ قَالَ ‏"‏ وَجَدْنَاهُ بَحْرًا ‏"‏‏.‏ أَوْ قَالَ ‏"‏ إِنَّهُ لَبَحْرٌ ‏"‏‏.‏
Reference : Sahih al-Bukhari 2908
In-book reference : Book 56, Hadith 121
USC-MSA web (English) reference : Vol. 4, Book 52, Hadith 156
  (deprecated numbering scheme)