Sahih Bukhari Volume 4, Book 52, Hadith Number 213.

Narated 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. (Qastalani Vol. 5)