Sahih Bukhari
Prophetic Commentary on the Quran (Tafseer of the Prophet (PBUH))
Volume: 006 / Book Number: 060 / Hadith Number: 227
Narrated Abu Huraira:
Allah's Apostle said, "The Um (substance) of the Quran is the seven oft-repeated verses (Al-Mathaini) and is the Great Quran (i.e. Surat-al-Fatiha)."