كتاب التفسير
65  
Prophetic Commentary on the Qur'an (Tafseer of the Prophet (pbuh))
(2)
"O you who believe! Answer Allah (by obeying Him) and (His) Messenger when he () calls you to that which will give you life, and know that Allah comes in between a man and his heart (i.e., He prevents an evil person to decide anything). And verily, to Him you shall (all) be gathered." (V.8:24)
(2)
Sahih al-Bukhari 4647

Narrated Abu Sa`id bin Al-Mu'alla:

While I was praying, Allah's Messenger (ﷺ) passed me and called me, but I did not go to him until I had finished the prayer. Then I went to him, and he said, "What prevented you from coming to me? Didn't Allah say:-- "O you who believe! Answer the call of Allah (by obeying Him) and His Apostle when He calls you?" He then said, "I will inform you of the greatest Sura in the Qur'an before I leave (the mosque)." When Allah's Messenger (ﷺ) got ready to leave (the mosque), I reminded him. He said, "It is: 'Praise be to Allah, the Lord of the worlds.' (i.e. Surat-al-Fatiha) As-sab'a Al-Mathani (the seven repeatedly recited Verses).

حَدَّثَنِي إِسْحَاقُ، أَخْبَرَنَا رَوْحٌ، حَدَّثَنَا شُعْبَةُ، عَنْ خُبَيْبِ بْنِ عَبْدِ الرَّحْمَنِ، سَمِعْتُ حَفْصَ بْنَ عَاصِمٍ، يُحَدِّثُ عَنْ أَبِي سَعِيدِ بْنِ الْمُعَلَّى ـ رضى الله عنه ـ قَالَ كُنْتُ أُصَلِّي فَمَرَّ بِي رَسُولُ اللَّهِ صلى الله عليه وسلم فَدَعَانِي فَلَمْ آتِهِ حَتَّى صَلَّيْتُ، ثُمَّ أَتَيْتُهُ فَقَالَ ‏"‏ مَا مَنَعَكَ أَنْ تَأْتِيَ أَلَمْ يَقُلِ اللَّهُ ‏{‏يَا أَيُّهَا الَّذِينَ آمَنُوا اسْتَجِيبُوا لِلَّهِ وَلِلرَّسُولِ إِذَا دَعَاكُمْ‏}‏ ثُمَّ قَالَ لأُعَلِّمَنَّكَ أَعْظَمَ سُورَةٍ فِي الْقُرْآنِ قَبْلَ أَنْ أَخْرُجَ ‏"‏‏.‏ فَذَهَبَ رَسُولُ اللَّهِ صلى الله عليه وسلم لِيَخْرُجَ فَذَكَرْتُ لَهُ‏.‏ وَقَالَ مُعَاذٌ حَدَّثَنَا شُعْبَةُ، عَنْ خُبَيْبٍ، سَمِعَ حَفْصًا، سَمِعَ أَبَا سَعِيدٍ، رَجُلاً مِنْ أَصْحَابِ النَّبِيِّ صلى الله عليه وسلم بِهَذَا، وَقَالَ هِيَ ‏{‏الْحَمْدُ لِلَّهِ رَبِّ الْعَالَمِينَ‏}‏ السَّبْعُ الْمَثَانِي‏.‏
Reference : Sahih al-Bukhari 4647
In-book reference : Book 65, Hadith 169
USC-MSA web (English) reference : Vol. 6, Book 60, Hadith 170
  (deprecated numbering scheme)