I was praying when the Messenger of Allah ﷺ called me, but I did not answer him until I had finished my prayer. Then I came to him.He asked, "What kept you from coming to me?"I said, "Messenger of Allah, I was praying."He said, "Did Allah not say, 'You who believe, respond to Allah and the Messenger when he calls you' [Anfal 8:24]?"Then he said, "I will surely teach you the greatest surah in the Quran," or, "of the Quran, before you leave the mosque."He took me by the hand, and when he was about to leave the mosque, I said, "Messenger of Allah, you said you would teach me the greatest surah in the Quran."He said, "Yes. Al-hamdu lillahi rabbi al-alamin. It is the seven oft-repeated verses and the Magnificent Quran which has been given to me."
حدثنا يحيى بن سعيد عن شعبة قال حدثني خبيب بن عبد الرحمن عن حفص بن عاصم
كنت أصلي فدعاني رسول الله ﷺ فلم أجبه حتى صليت فأتيته فقال ما منعك أن تأتيني قال قلت يا رسول الله إني كنت أصلي قال ألم يقل الله عز وجل {يا أيها الذين آمنوا استجيبوا لله وللرسول إذا دعاكم} ثم قال لأعلمنك أعظم سورة في القرآن أو من القرآن قبل أن تخرج من المسجد قال فأخذ بيدي فلما أراد أن يخرج من المسجد قلت يا رسول الله إنك قلت لأعلمنك أعظم سورة في القرآن قال نعم الحمد لله رب العالمين هي السبع المثاني والقرآن العظيم الذي أوتيته
Its isnad is sahih, its narrators are famous and trustworthy. The hadith was narrated by Bukhari 6/20 (Shaab edition) in the tafsir of the Fatihah, Nasai 2/139 in the Opening, Ibn Majah 2/1244, no. 3785, in Manners, on the reward of the Quran, and Darimi 2/538, no. 2371, in the Virtues of the Quran, on the merit of the Fatihah. And Bayhaqi 7/64.