Musnad Abu Ya'la al-Mawsili 3:58

Ubayd Allah narrated to us, saying: Yazid bin Zuray' and Muhammad bin Ja'far narrated to us, saying: Shu'bah narrated to us, from Abu Ishaq, who said: I heard 'Asim bin Damrah saying: We asked 'Ali about the prayer of the Messenger of Allah (may Allah bless him and grant him peace) during the day. He said: "Indeed, you cannot endure that." We said: "Who among us can endure that?" He said: "When the sun was from here, like its position from here at the time of 'Asr, he would pray two rak'ahs. And when the sun was from here, like its position from here at the time of Dhuhr, he would pray four rak'ahs, separating between every two rak'ahs with the taslim upon the angels brought near, the prophets, and those who followed them from the prophets and the messengers."