Sahih al-Bukhari 4163
Narrated Tariq bin `Abdur-Rahman:
When I set out for Hajj, I passed by some people offering a prayer, I asked, "What is this mosque?" 
They said, "This is the Tree where Allah's Messenger (ﷺ) took the Ar-Ridwan Pledge of allegiance. Then I 
went to Sa`id bin Musaiyab and informed him about it. Sa`id said, "My father said that he was 
amongst those who had given the Pledge of allegiance to Allah's Messenger (ﷺ) beneath the Tree. He (i.e. my 
father) said, "When we set out the following year, we forgot the Tree and were unable to recognize it. 
"Then Sa`id said (perhaps ironically) "The companions of the Prophet (ﷺ) could not recognize it; 
nevertheless, you do recognize it; therefore you have a better knowledge."
حَدَّثَنَا مَحْمُودٌ، حَدَّثَنَا عُبَيْدُ اللَّهِ، عَنْ إِسْرَائِيلَ، عَنْ طَارِقِ بْنِ عَبْدِ الرَّحْمَنِ، قَالَ انْطَلَقْتُ حَاجًّا فَمَرَرْتُ بِقَوْمٍ يُصَلُّونَ قُلْتُ مَا هَذَا الْمَسْجِدُ قَالُوا هَذِهِ الشَّجَرَةُ، حَيْثُ بَايَعَ رَسُولُ اللَّهِ صلى الله عليه وسلم بَيْعَةَ الرُّضْوَانِ‏.‏ فَأَتَيْتُ سَعِيدَ بْنَ الْمُسَيَّبِ فَأَخْبَرْتُهُ فَقَالَ سَعِيدٌ حَدَّثَنِي أَبِي أَنَّهُ كَانَ فِيمَنْ بَايَعَ رَسُولَ اللَّهِ صلى الله عليه وسلم تَحْتَ الشَّجَرَةِ، قَالَ فَلَمَّا خَرَجْنَا مِنَ الْعَامِ الْمُقْبِلِ نَسِينَاهَا، فَلَمْ نَقْدِرْ عَلَيْهَا‏.‏ فَقَالَ سَعِيدٌ إِنَّ أَصْحَابَ مُحَمَّدٍ صلى الله عليه وسلم لَمْ يَعْلَمُوهَا وَعَلِمْتُمُوهَا أَنْتُمْ، فَأَنْتُمْ أَعْلَمُ‏.‏