Sahih Muslim Book 004, Hadith Number 1740.
Chapter : The recitation by the Apostle (may peace be upon him) of Surat al-Fath on the Day of the Conquest of Mecca.
Ibn Ishaq reported: I heard al-Bara' as saying that a man recited al-Kahf when an animal was there in the house and it began to take fright. And as he looked around, he found a cloud overshadowing it. He mentioned that to the Apostle of Allah (may peace be upon him). Upon this he said: O so and so, recite on (the surah) as-Sakina descends at the (recitation of the Qur'an) or on account (of the recitation) of the Qur'an.