Sahih Bukhari Volume 5, Book 59, Hadith Number 480.

Narrated By Said bin Al-Musaiyab : That his father said, “I saw the Tree (of the Ar-Ridwan Pledge of allegiance and when I returned to it later, I was not able to recognize it. (The sub-narrator MahmiJd said, Al-Musaiyab said, ‘Then; forgot it (i.e., the Tree).)”