A man was reciting Surah al-Kahf when there was an animal in the house that began to bolt in fright. He looked up and saw a mist, or a cloud, that had enveloped him. He mentioned this to the Prophet ﷺ, who said, "Keep reciting, so-and-so, for that was tranquility descending at the recitation of the Quran," or, "descending for the Quran."
حدثنا محمد بن جعفر حدثنا شعبة عن أبي إسحاق قال سمعت
قرأ رجل الكهف وفي الدار دابة فجعلت تنفر فنظر فإذا ضبابة أو سحابة قد غشيته قالا فذكر ذلك للنبي ﷺ فقال اقرأ فلان فإنها السكينة تنزلت عند القرآن أو تنزلت للقرآن
Its isnad is sahih. Reported by Muslim, 1/547, no. 795, in "the travelers," "the descent of tranquility for the Quran," and similarly by Bukhari, 4/245, Shaab edition, in "virtues," "signs of prophethood," and by Tirmidhi, 5/161, no. 2885, who said, hasan sahih.