كتاب التفسير
65
Prophetic Commentary on the Qur'an (Tafseer of the Prophet (pbuh))
(4)
"He it is Who sent down As-Sakīnah (tranquillity and calmness) into the hearts of the believers..." (V.48:4)
(4)
Sahih al-Bukhari 4839

Narrated Al-Bara:

While a man from the companions of the Prophet (ﷺ) 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 (ﷺ) said, "That was the tranquility (calmness) which descended because of the recitation of the Qur'an."

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 ‏"‏‏.‏
Reference : Sahih al-Bukhari 4839
In-book reference : Book 65, Hadith 360
USC-MSA web (English) reference : Vol. 6, Book 60, Hadith 363
  (deprecated numbering scheme)