Sahih Muslim
The Book of Prayers (Kitab Al-Salat)
Book Number: 004 / Hadith Number: 908
Abu Qatada reported: The Messenger of Allah (may peace be upon him) led us in prayer and recited in the first two rak'ahs of the noon and afternoon prayers Surat al-Fitiha and two (other) surahs. And he would sometimes recite loud enough for us the verses. He would prolong the first rak'ah more than the second. And he acted similarly in the morning prayer.