Musannaf Ibn Abi Shayba 3:5425

Waki’ narrated to us, he said: Yusuf ibn Suhayb narrated to us, from Habib ibn Yasar, from Abu Ramla al-Azdi, that Ali saw them praying the Duha (forenoon) prayer when the sun was rising. He said: "Why did they not leave it until, when the sun was the height of a spear or two spears, they prayed it? For that is the prayer of the oft-returning (al-awwabin)."