Sahih al-Bukhari 4703
Sahih al-Bukhari · Book 65: Prophetic Commentary on the Qur'an (Tafseer of the Prophet (pbuh)) · The Statement of Allah "And indeed, We have bestowed upon you seven Al-Mathãni (i.e., seven repeatedly recited Verses i.e., Sürat AI-Fatiha) and the Grand Qur'an." (V.15:87)
Narrated Abu Sa`id Al-Mualla:
حَدَّثَنِي مُحَمَّدُ بْنُ بَشَّارٍ ، حَدَّثَنَا غُنْدَرٌ ، حَدَّثَنَا شُعْبَةُ ، عَنْ خُبَيْبِ بْنِ عَبْدِ الرَّحْمَنِ ، عَنْ حَفْصِ بْنِ عَاصِمٍ ، عَنْ أَبِي سَعِيدِ بْنِ الْمُعَلَّى ، قَالَ مَرَّ بِيَ النَّبِيُّ صلى الله عليه وسلم وَأَنَا أُصَلِّي فَدَعَانِي فَلَمْ آتِهِ حَتَّى صَلَّيْتُ ثُمَّ أَتَيْتُ فَقَالَ " مَا مَنَعَكَ أَنْ تَأْتِيَ ". فَقُلْتُ كُنْتُ أُصَلِّي. فَقَالَ " أَلَمْ يَقُلِ اللَّهُ {يَا أَيُّهَا الَّذِينَ آمَنُوا اسْتَجِيبُوا لِلَّهِ وَلِلرَّسُولِ} ثُمَّ قَالَ أَلاَ أُعَلِّمُكَ أَعْظَمَ سُورَةٍ فِي الْقُرْآنِ قَبْلَ أَنْ أَخْرُجَ مِنَ الْمَسْجِدِ " فَذَهَبَ النَّبِيُّ صلى الله عليه وسلم لِيَخْرُجَ مِنَ الْمَسْجِدِ فَذَكَّرْتُهُ فَقَالَ " {الْحَمْدُ لِلَّهِ رَبِّ الْعَالَمِينَ} هِيَ السَّبْعُ الْمَثَانِي وَالْقُرْآنُ الْعَظِيمُ الَّذِي أُوتِيتُهُ " .
While I was praying, the Prophet (ﷺ) passed by and called me, but I did not go to him till I had finished my prayer. When I went to him, he said, "What prevented you from coming?" I said, "I was praying." He said, "Didn't Allah say" "O you who believes Give your response to Allah (by obeying Him) and to His Apostle." (8.24) Then he added, "Shall I tell you the most superior Sura in the Qur'an before I go out of the mosque?" When the Prophet (ﷺ) intended to go out (of the Mosque), I reminded him and he said, "That is: "Al hamdu-li l-lahi Rabbil-`alamin (Surat-al-fatiha)' which is the seven oft repeated verses (Al-Mathani) and the Grand Qur'an which has been given to me."