Musnad Abu Ya'la al-Mawsili 3:74

Ubayd Allah narrated to us, Hisham ibn Abd al-Malik narrated to us, Shu'bah narrated to us, from Abu Ishaq, from Asim ibn Damrah, from Ali: That the Messenger of Allah (peace and blessings of Allah be upon him) used to pray the Duha (forenoon) prayer.