Sunan Abi Dawud Book 2, Hadith 433
We were behind the Messenger of Allah (ﷺ) at the dawn prayer, and he recited (the passage), but the recitation became difficult for him. Then when he finished, he said: Perhaps you recite behind your imam? We replied: Yes, it is so, Messenger of Allah. He said: Do not do so except when it is Fatihat al-Kitab, for he who does not recite it is not credited with having prayed.
the prayer is not valid I one does not recite fatihat al-kitab and something more, sufyan( the narrator) said: This applies to a man who prays alone.
“Ubadah b. al-samit came to late to lead the morning prayer. Abu Nu’aim, the mu’adhdhin, pronounced the takbir and he led the people in prayer. Then Ubadah came and I was with him. We Joined the row behind Abu Nu’aim, while Abu Nu’aim was reciting the Qur’an loudly. Then ‘Ubadah began to recite the Umm al-Quran (I.e Surah al Fatihah). When he finished, I said to Ubadah: I heard you reciting the Umm al-Qur’an while Abu Nu’aim was reciting Qur’an loudly. He replied: yes> The Messenger of Allah (ﷺ) led us in a certain prayer in which the Qur’an is recited loudly, but he became confused in the recitation. When he finished he turned his face to us and said: Do you recite when I recite the Qur’an loudly? Some of us said: we do so; this is why I said to myself: What is that which confused me (in the recitation of ) the Qur’an. Do not recite anything from the Qur’an when I recite it loudly except the Umm al-Qur’an.