Musnad Ahmad 1007:142

Ad-Dahhak ibn Makhlad narrated to us, from Al-Awza'i, Yahya ibn Abi Kathir narrated to me, Abdullah ibn Abi Qatadah narrated to us, Abu Qatadah narrated to me—or he said: We were narrated to—that the Messenger of Allah (peace and blessings of Allah be upon him) used to recite in the two rak'ahs of the Dhuhr prayer the Opening of the Book (Al-Fatihah) and a surah, and he would prolong the first two [rak'ahs]. And in the 'Asr prayer, it was like that, and he would let us hear the verse sometimes.