Sahih Al Bukhari Hadith Number 1103

Narrated Ibn Abu Laila: Only Um Hani told us that she had seen the Prophet (peace be upon him) offering the Duha (forenoon prayer). She said, “On the day of the conquest of Mecca, the Prophet (peace be upon him) took a bath in my house and offered eight rak`at. I never saw him praying such a light prayer but he performed perfect prostration and bowing.

18  Shortening the Prayers (At-Taqseer)
Hadith number 1103
Volume no 2
Chapter: 12 (Whoever offered Nawafil not after the compulsory Salat but before it)