Sahih al-Bukhari — Military Expeditions led by the Prophet (pbuh) (Al-Maghaazi) — Hadith No: 4162
Translation
Narrated Sa`id 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 Mahmud said, Al-Musaiyab said, 'Then I forgot it (i.e., the Tree)