Musnad Ahmad 1166:12

Ya'la ibn 'Ubayd narrated to us, he said: Isma'il—meaning Ibn Abi Khalid—narrated to us, from Abu Salih, from Umm Hani, who said: "When the Messenger of Allah, peace and blessings of Allah be upon him, entered on the day of the conquest of Makkah, they screened him. Water was brought, and he performed ghusl (a full ritual bath). Then he prayed the Duha (forenoon) prayer, eight rak'ahs. No one saw him pray them after that."