Musnad Ahmad 1012:80

Ya'qub narrated to us, my father narrated to us, from Ibn Ishaq, Makhul narrated to me, from Mahmud ibn al-Rabi' al-Ansari, from 'Ubadah ibn al-Samit, who said: The Messenger of Allah (peace and blessings of Allah be upon him) led us in the morning prayer, and the recitation became difficult for him during it. When the Messenger of Allah (peace and blessings of Allah be upon him) finished his prayer, he turned his face toward us and said: "I see you reciting behind your Imam when he recites aloud." We said: "Yes, by Allah, O Messenger of Allah, we do that." The Messenger of Allah (peace and blessings of Allah be upon him) said: "Do not do so, except for the Mother of the Qur'an (Al-Fatiha), for there is no prayer for the one who does not recite it."