Musnad Ahmad 5:637

Abdullah narrated to us, Abu Kamil al-Jahdari Fudayl ibn al-Husayn narrated to us, dictating to me from his book, Abu 'Awanah narrated to us, from Abu Ishaq, from 'Asim ibn Damrah, from 'Ali: That he was asked about the prayer of the Messenger of Allah, peace and blessings of Allah be upon him, during the day. He said: "He used to pray sixteen rak'ahs." He said: "He would pray when the sun was from here, like its position from here, like the time of the 'Asr prayer, two rak'ahs. And he would pray when the sun was from here, like its position from here, like the time of the Dhuhr prayer, four rak'ahs. And he would pray before Dhuhr four rak'ahs, and after Dhuhr two rak'ahs, and before 'Asr four rak'ahs."