Bukhari Collection: ::Book Number 4:: Hadith # 811
Narrated Al-Bara' bin `Azib:A man recited Surat-al-Kahf (in his prayer) and in the house there was a (riding) animal which got frightened and started jumping. The man finished his prayer with Taslim, but behold! A mist or a cloud hovered over him. He informed the Prophet of that and the Prophet said, "O so-and-so! Recite, for this (mist or cloud) was a sign of peace descending for the recitation of Qur'an."