Narrated Abu Said Al-Mualla:
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 intended to go out (of the Mosque), I reminded him and he said, "That is: "Alhamdu-lillahi Rabbil-'Alamin (Surat-al-fatiha)' which is the seven oft repeated verses (Al-Mathani) and the Grand Quran which has been given to me."
Sahih al-Bukhari, Vol. 6, Book of Prophetic Commentary on the Qur'an, Hadith 226
Sahih al-Bukhari, Book of Prophetic Commentary on the Qur'an, Hadith 226