Sahih Bukhari Volume 008, Book 073, Hadith Number 059B.

Narated By Anas : The Prophet was the best among the people (both in shape and character) and was the most generous of them, and was the bravest of them. Once, during the night, the people of Medina got afraid (of a sound). So the people went towards that sound, but the Prophet having gone to that sound before them, met them while he was saying, "Don't be afraid, don't be afraid." (At that time) he was riding a horse belonging to Abu Talha and it was naked without a saddle, and he was carrying a sword slung at his neck. The Prophet said, "I found it (the horse) like a sea, or, it is the sea indeed."