Sahih Bukhari
Characteristics of Prayer
Volume: 001 / Book Number: 012 / Hadith Number: 729
Narrated 'Abdullah bin Abi Qatada:
My father said, "The Prophet used to recite Al-Fatiha along with another Sura in the first two Rakat of the Zuhr and the 'Asr prayers and at times a t verse or so was audible to us."