Abu Sa’id ibn al-Mu’alla reported: I was praying in the mosque when the Messenger of Allah, peace and blessings be upon him, called out to me but I did not respond. I said later, “O Messenger of Allah, I was praying.” The Prophet said, “Did not Allah say: Respond to Allah and the Messenger when he calls you?” (8:24) Then, the Prophet said, “Shall I not teach you the greatest chapter in the Quran before you leave the mosque?” The Prophet took me by the hand and when he intended to leave, I said to him, “Did you not say that you would teach me the greatest chapter in the Quran?” The Prophet said, “All praise is due to Allah, the Lord of the worlds (1:1), which are the seven oft-repeated verses and the great Quran given to me.”
Source: Ṣaḥīḥ al-Bukhārī 5006
Grade: Sahih (authentic) according to Al-Bukhari
عَنْ أَبِي سَعِيدِ بْنِ الْمُعَلَّى قَالَ كُنْتُ أُصَلِّي فَدَعَانِي النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَلَمْ أُجِبْهُ قُلْتُ يَا رَسُولَ اللَّهِ إِنِّي كُنْتُ أُصَلِّي قَالَ أَلَمْ يَقُلْ اللَّهُ اسْتَجِيبُوا لِلَّهِ وَلِلرَّسُولِ إِذَا دَعَاكُمْ ثُمَّ قَالَ أَلَا أُعَلِّمُكَ أَعْظَمَ سُورَةٍ فِي الْقُرْآنِ قَبْلَ أَنْ تَخْرُجَ مِنْ الْمَسْجِدِ فَأَخَذَ بِيَدِي فَلَمَّا أَرَدْنَا أَنْ نَخْرُجَ قُلْتُ يَا رَسُولَ اللَّهِ إِنَّكَ قُلْتَ لَأُعَلِّمَنَّكَ أَعْظَمَ سُورَةٍ مِنْ الْقُرْآنِ قَالَ الْحَمْدُ لِلَّهِ رَبِّ الْعَالَمِينَ هِيَ السَّبْعُ الْمَثَانِي وَالْقُرْآنُ الْعَظِيمُ الَّذِي أُوتِيتُهُ
5006 صحيح البخاري كتاب فضائل القرآن باب فضل فاتحة الكتاب