Abu Saeed bin Mualla reported,
The Prophet ﷺ passed by him while he was praying and called him. He said, "I finished my prayer and then went to him."The Prophet ﷺ asked, "What prevented you from answering me?"He replied, "I was praying."The Prophet ﷺ said, "Did Allah 
not say, 'O you who believe, respond to Allah and the Messenger when he calls you to that which gives you life' [Anfal 8:24]? Shall I teach you the greatest surah before I leave the mosque?"He started to leave, and I said, "Messenger of Allah, what about what you said?"He answered, "Praise be to Allah, Lord of the worlds. It is the seven oft-repeated verses and the Magnificent Quran that has been given to me."
Nasai 914
Sahihأخبرنا إسمعيل بن مسعود قال حدثنا خالد قال حدثنا شعبة عن خبيب بن عبد الرحمن قال سمعت حفص بن عاصم يحدث
عن أبي سعيد بن المعل
ى أن النبي ﷺ مر به وهو يصلي فدعاه قال فصليت ثم أتيته فقال ما منعك أن تجيبني قال كنت أصلي قال ألم يقل الله عز وجل {يا أيها الذين آمنوا استجيبوا لله وللرسول إذا دعاكم لما يحييكم} ألا أعلمك أعظم سورة قبل أن أخرج من المسجد قال فذهب ليخرج قلت يا رسول الله قولك قال الحمد لله رب العالمين هي السبع المثاني الذي أوتيت والقرآن العظيم
, "And We have certainly given you seven of the often repeated verses and the great Quran", "And We have certainly given you seven of the often repeated verses and the great Quran"Bukhari narrated it in the Book of Tafsir, chapter on what has been said about the Opening of the Book, hadith 4474, from the hadith of Shubah with this chain, and it is also in Sunan al-Kubra, hadith 985.