Sahih Al Bukhari – Book of Characteristics Of Prayer

Volumn 001, Book 012, Hadith Number 745.
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Narated By 'Abdullah bin Abi Qatada RA : My father said, "The Prophet PBUH used to recite Al-Fatiha along with another Sura in the first two Rakat of the Zuhr and 'Asr prayers. A verse or so was audible at times and he used to prolong the first Rak'a."