Musnad Ahmad 1007:54

Isma'il narrated to us, Hisham al-Dastawa'i informed us, Yahya ibn Abi Kathir narrated to me, from 'Abdullah ibn Abi Qatadah, from his father, who said: The Messenger of Allah (peace and blessings of Allah be upon him) used to recite for us in the first two rak'ahs of the Dhuhr prayer, and he would let us hear the verse sometimes. He would prolong the first and shorten the second. He used to do that in the Subh (morning) prayer; he would prolong the first and shorten the second. And he used to recite for us in the first two rak'ahs of the 'Asr prayer.