Sahih Muslim 795 b
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 Messenger of Allah (ﷺ). 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.
وَحَدَّثَنَا ابْنُ الْمُثَنَّى، وَابْنُ، بَشَّارٍ - وَاللَّفْظُ لاِبْنِ الْمُثَنَّى - قَالاَ حَدَّثَنَا مُحَمَّدُ بْنُ، جَعْفَرٍ حَدَّثَنَا شُعْبَةُ، عَنْ أَبِي إِسْحَاقَ، قَالَ سَمِعْتُ الْبَرَاءَ، يَقُولُ قَرَأَ رَجُلٌ الْكَهْفَ وَفِي الدَّارِ دَابَّةٌ فَجَعَلَتْ تَنْفِرُ فَنَظَرَ فَإِذَا ضَبَابَةٌ أَوْ سَحَابَةٌ قَدْ غَشِيَتْهُ قَالَ فَذَكَرَ ذَلِكَ لِلنَّبِيِّ صلى الله عليه وسلم فَقَالَ ‏
"‏ اقْرَأْ فُلاَنُ فَإِنَّهَا السَّكِينَةُ تَنَزَّلَتْ عِنْدَ الْقُرْآنِ أَوْ تَنَزَّلَتْ لِلْقُرْآنِ ‏"‏ ‏.‏