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-ʿalamin (Surat-al-fatiha)' which is the seven oft repeated verses (Al-Mathani) and the Grand Qur'an which has been given to me." (Using translation from Bukhārī 4703)
مَرَّ بِي رَسُولُ اللهِ ﷺ وَأَنَا أُصَلِّي فَدَعَانِي فَلَمْ آتِهِ حَتَّى صَلَّيْتُ ثُمَّ أَتَيْتُهُ فَقَالَ لِي «مَا مَنَعَكَ أَنْ تَأْتِيَنِي؟» قُلْتُ كُنْتُ أُصَلِّي فَقَالَ أَلَمْ يَقِلِ اللهُ ﷻ {يَا أَيُّهَا الَّذِينَ آمَنُوا اسْتَجِيبُوا لِلَّهِ وَلِلرَّسُولِ} [الأنفال 24]؟ قَالَ «أَلَا أُعَلِّمُكَ أَعْظَمَ سُورَةٍ فِي الْقُرْآنِ قَبْلَ أَنْ أَخْرُجَ مِنَ الْمَسْجِدِ؟» فَذَهَبَ لِيُخْرِجَ فَذَكَّرْتُهُ فَقَالَ «الْحَمْدُ لِلَّهِ رَبِّ الْعَالَمِينَ هِيَ السَّبْعُ الْمَثَانِي وَالْقُرْآنُ الْعَظِيمُ الَّذِي أُوتِيتُهُ»