Language:
كتاب المغازى
64  
Military Expeditions led by the Prophet (pbuh) (Al-Maghaazi)
(35)
Chapter: The Ghazwa of Al-Hudaibiya
(35)
باب غَزْوَةِ الْحُدَيْبِيَةِ
Sahih al-Bukhari 4162

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 MahmiJd said, Al-Musaiyab said, 'Then; forgot it (i.e., the Tree).)"

حَدَّثَنِي مُحَمَّدُ بْنُ رَافِعٍ، حَدَّثَنَا شَبَابَةُ بْنُ سَوَّارٍ أَبُو عَمْرٍو الْفَزَارِيُّ، حَدَّثَنَا شُعْبَةُ، عَنْ قَتَادَةَ، عَنْ سَعِيدِ بْنِ الْمُسَيَّبِ، عَنْ أَبِيهِ، قَالَ لَقَدْ رَأَيْتُ الشَّجَرَةَ، ثُمَّ أَتَيْتُهَا بَعْدُ فَلَمْ أَعْرِفْهَا‏.‏ قَالَ مَحْمُودٌ ثُمَّ أُنْسِيتُهَا بَعْدُ‏.‏
Reference : Sahih al-Bukhari 4162
In-book reference : Book 64, Hadith 204
USC-MSA web (English) reference : Vol. 5, Book 59, Hadith 480
  (deprecated numbering scheme)