Sahih Bukhari
Characteristics of Prayer
Volume: 001 / Book Number: 012 / Hadith Number: 743
Narrated 'Abdullah bin Abi Qatada:
My father said, "The Prophet uses to recite Al-Fatiha followed by another Sura in the first two Rakat of the prayer and used to recite only Al-Fatiha in the last two Rakat of the Zuhr prayer. Sometimes a verse or so was audible and he used to prolong the first Rak'a more than the second and used to do the same in the 'Asr and Fajr prayers."