Sahih Bukhari Volume 6, Book 65, Hadith 4841

حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ مُوسَى، عَنْ إِسْرَائِيلَ، عَنْ أَبِي إِسْحَاقَ، عَنِ الْبَرَاءِ ـ رضى الله عنه ـ قَالَ بَيْنَمَا رَجُلٌ مِنْ أَصْحَابِ النَّبِيِّ صلى الله عليه وسلم يَقْرَأُ، وَفَرَسٌ لَهُ مَرْبُوطٌ فِي الدَّارِ، فَجَعَلَ يَنْفِرُ، فَخَرَجَ الرَّجُلُ فَنَظَرَ فَلَمْ يَرَ شَيْئًا، وَجَعَلَ يَنْفِرُ، فَلَمَّا أَصْبَحَ ذَكَرَ ذَلِكَ لِلنَّبِيِّ صلى الله عليه وسلم فَقَالَ ‏"‏ تِلْكَ السَّكِينَةُ تَنَزَّلَتْ بِالْقُرْآنِ ‏"‏‏.‏

Narrated By Al-Bara : While a man from the companions of the Prophet was reciting (Qur'an) 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 tranquillity (calmness) which descended because of the recitation of the Qur'an."