Mishkat al-Masabih 775

Abu Qatada said that in the first two rak'as of the noon prayer the Prophet used to recite Umm al-Kitab and two suras, and in the last two rak'as Umm al-Kitab, and he would sometimes recite loud enough for them to hear the verse. He would prolong the first rak'a more than the second; and he acted similarly in the afternoon and the Morning Prayer. (Bukhari and Muslim.)