Musnad Ahmad 1272:13

Ubaydah ibn Humayd narrated to us, he said: Yazid ibn Abi Ziyad narrated to me, from Abdullah ibn al-Harith, he said: I asked him about the Duha (forenoon) prayer, and he said: I asked the companions of the Messenger of Allah, peace and blessings of Allah be upon him, about it, but I did not find anyone who could inform me that the Messenger of Allah, peace and blessings of Allah be upon him, prayed it. Except that Umm Hani informed me: "That the Messenger of Allah, peace and blessings of Allah be upon him, entered upon her and prayed eight rak'ahs, and I did not see him pray them before or after."