I was praying in the mosque when the Messenger of Allah ﷺ called me, but I did not answer him.Then I said, "Messenger of Allah, I was praying."He 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]?"Then he said to me, "I will surely teach you a surah that is the greatest surah in the Quran before you leave the mosque."Then he took me by the hand, and when he was about to leave, I said to him, "Did you not say, 'I will teach you a surah that is the greatest surah in the Quran'?"He said, "'Praise be to Allah, Lord of the worlds' [Fatihah 1:2]. It is the seven oft-repeated verses and the Mighty Quran that I have been given."
كنت أصلي في المسجد، فدعاني رسول الله ﷺ، فلم أجبه، فقلت: يا رسول الله! إني كنت أصلي فقال: ألم يقل الله: {يأيها الذين آمنوا استجيبوا لله وللرسول إذا دعاكم لما يحييكم}، ثم قال لي: لأعلمنك سورة هي أعظم السور في القرآن قبل أن تخرج من المسجد. ثم أخذ بيدي، فلما أراد أن يخرج قلت له: ألم تقل: لأعلمنك سورة هي أعظم سورة في القرآن. قال: {الحمد لله رب العلمين} هي السبع المثاني، والقرآن العظيم الذي أوتيته.
Bukhari related it in the tafsir (4474), from Musaddad, who said, Yahya narrated to us, from Shubah, who said, Khubayb bin Abdul-Rahman narrated to me, from Hafs bin Asim, from Abu Saeed bin Mualla, and he mentioned it.