كتاب التفسير
65
Prophetic Commentary on the Qur'an (Tafseer of the Prophet (pbuh))
(3)
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)
(3)
Sahih al-Bukhari 4704

Narrated Abu Huraira:

Allah's Messenger (ﷺ) said, "The Um (substance) of the Qur'an is the seven oft-repeated verses (Al- Mathaini) and is the Great Qur'an (i.e. Surat-al-Fatiha).

حَدَّثَنَا آدَمُ، حَدَّثَنَا ابْنُ أَبِي ذِئْبٍ، حَدَّثَنَا سَعِيدٌ الْمَقْبُرِيُّ، عَنْ أَبِي هُرَيْرَةَ ـ رضى الله عنه ـ قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ أُمُّ الْقُرْآنِ هِيَ السَّبْعُ الْمَثَانِي وَالْقُرْآنُ الْعَظِيمُ ‏"‏‏.‏
Reference : Sahih al-Bukhari 4704
In-book reference : Book 65, Hadith 226
USC-MSA web (English) reference : Vol. 6, Book 60, Hadith 227
  (deprecated numbering scheme)