Reciting Surah al-Fatihah behind the Imam:
إِسْمَاعِيل بْنُ عُلَيَّةَ، ‏‏‏‏‏‏عَنْ ابْنِ جُرَيْجٍ، ‏‏‏‏‏‏عَنْ الْعَلَاءِ بْنِ عَبْدِ الرَّحْمَنِ بْنِ يَعْقُوبَ، ‏‏‏‏‏‏أَنَّ أَبَا السَّائِبِ، ‏‏‏‏‏‏أَخْبَرَهُ أَنَّهُ سَمِعَ أَبَا هُرَيْرَةَ، ‏‏‏‏‏‏يَقُولُ:‏‏‏‏
قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ:‏‏‏‏ مَنْ صَلَّى صَلَاةً لَمْ يَقْرَأْ فِيهَا بِأُمِّ الْقُرْآنِ، ‏‏‏‏‏‏فَهِيَ خِدَاجٌ غَيْرُ تَمَامٍ، ‏‏‏‏‏‏فَقُلْتُ:‏‏‏‏ يَا أَبَا هُرَيْرَةَ، ‏‏‏‏‏‏فَإِنِّي أَكُونُ أَحْيَانًا وَرَاءَ الْإِمَامِ، ‏‏‏‏‏‏فَغَمَزَ ذِرَاعِي وَقَالَ:‏‏‏‏ يَا فَارِسِيُّ، ‏‏‏‏‏‏اقْرَأْ بِهَا فِي نَفْسِكَ.
Abu Bakr ibn Abi Shaybah narrated to us, Isma‘il ibn ‘Ulayyah narrated to us, from Ibn Jurayj, from al-‘Ala ibn ‘Abd al-Rahman ibn Ya‘qub, that Abu al-Sa’ib informed him that he heard Abu Hurayrah say:
The Messenger of Allah (may Allah bless him and give him peace) said:
“Whoever performs a prayer in which he does not recite Umm al-Qur’an (al-Fatihah), then it is incomplete – not complete.”
So I said: “O Abu Hurayrah, sometimes I am behind the Imam.” He nudged my arm and said: “O Persian, recite it within your heart.”
(Sunan Ibn Majah, 838)