Sayyiduna Ubadah bin Samit (may Allah be pleased with him) narrates: Once the Prophet Muhammad (peace be upon him) led us in the morning prayer. It became difficult for him to recite (Qur'an). When he completed the prayer, he said: I think you recite behind your Imam as well. The narrator says: We said: Yes, O Messenger of Allah! That is so. The Prophet Muhammad (peace be upon him) said: Do not do so. You should recite Surah Al-Fatihah. The prayer of the one who does not recite it is not valid.