Sahih Muslim, Chapter: Prayers (Kitab Al-Salat)

on the authority of Abu Huraira who said that one should recite (al-’Fatiha) in every (rak'ah of) prayer. What we heard (i. e. recitation) from the Messenger of Allah (may peace be upon him), we made you listen to that. And that which he (recited) inwardly, we (recited) inwardly for you. A person said to him: If I add nothing to the (recitation) of the Umm al Qur'an (Surat al-’Fatiha), would it make the prayer incomplete? He (AbuHuraira) said: If you add to that (if you recite some of verses of the Qur'an along with Surat at-’Fatiha) that is better for you. But if you are contented with it (Surat al-’Fatiha) only, it is sufficient for you.