That his father was amongst those who had given the Pledge of allegiance (to the Prophet (ﷺ) ) beneath the Tree, and the next year when they went towards the Tree, they were not able to recognize it.
Sahih al-Bukhari Book 64, Hadith 206
← Previous Hadith 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."

Sahih al-Bukhari Book 64, Hadith 205 Next Hadith → (The tree where the Ridwan Pledge of allegiance was taken by the Prophet) was mentioned before Sa`id bin Al-Musaiyab. On that he smiled and said, "My father informed me (about it) and he had witnessed it (i.e. the Pledge) ."

Sahih al-Bukhari Book 64, Hadith 207