Musnad Ahmad 1012:85

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 (may Allah bless him and grant him peace) led us in the morning prayer, and the recitation became difficult for him. When the Messenger of Allah (may Allah bless him and grant him peace) 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, this is so." He 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."