Sahih Bukhari Volume 2, Book 21, Hadith Number 272.

Narated By ‘Abdur Rahman bin Abi Laila : Only Um Hani narrated to me that she had seen the Prophet offering the Duha prayer. She said, “On the day of the conquest of Mecca, the Prophet entered my house, took a bath and offered eight Rakat (of Duha prayers. I had never seen the Prophet offering such a light prayer but he performed bowing and prostrations perfectly.