Sunan An-Nasai, Chapter: The Book of Leading the Prayer (Al-Imamah)

that Asim bin Damrah said: "We asked Ali about the prayer of the Messenger of Allah (saw). He said: 'Who among you could manage to do that?' We said; 'Even if we cannot do it, we still want to hear about it.' He said: 'When the sun reached the same height (in the east) as it reaches (in the west) at the time of Asr, he would pray two Rakahs,* and when the sun reached the same height (in the east) as it reaches (the west) at the time for Zuhr he would pray four Rakahs. He would pray four Rakahs before Zuhr and two after, and he would pray four Rakahs before Asr, separating each two Rakahs with Taslim upon the angels who are close to Allah, and the prophets, and those who follow them of the believers and Muslims.'" (Sahih) *That is, the Duha prayer.