Sahih Bukhari Volume 6, Book 60, Hadith Number 363.

Narrated By Al-Bara : While a man from the companions of the Prophet was reciting (Quran) and his horse was tied in the house, the horse got startled and started jumping. The man came out, looked around but could not find anything, yet the horse went on jumping. The next morning he mentioned that to the Prophet. The Prophet said, “That was the tranquility (calmness) which descended because of the recitation of the Quran.”