Sahih Al Bukhari Hadith Number 776

Narrated `Abdullah bin Abi Qatada: My father said, “The Prophet (peace be upon him) uses to recite Al-Fatiha followed by another Sura in the first two rak`at of the prayer and used to recite only Al-Fatiha in the last two rak`at 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.”

10  Call to Prayers (Adhaan)
Hadith number 776
Volume no 1
Chapter: 107 (To recite only Surah Al-Fathiha in the last two Rak’a during a four Rak’a Salat (prayer)