that Thabit bin Ad-Dahhak had informed him that he was one of those who had given the Pledge of allegiance (of Al-Hudaibiya) beneath the Tree.
Sahih al-Bukhari Book 64, Hadith 213
← Previous Hadith I met Al-Bara bin `Azib and said (to him). "May you live prosperously! You enjoyed the company of the Prophet (ﷺ) and gave him the Pledge of allegiance (of Al-Hudaibiya) under the Tree." On that, Al- Bara' said, "O my nephew! You do not know what we have done after him (i.e. his death).

Sahih al-Bukhari Book 64, Hadith 212 Next Hadith → regarding Allah's Statement: "Verily! We have granted you (O, Muhammad) Manifest victory." (48.1) It refers to the Al-Hudaibiya Pledge. And the companions of the Prophet (ﷺ) said (to the Prophet), "Congratulations and happiness for you; but what reward shall we get?" So Allah revealed:-- "That He may admit the believing men and women to gardens beneath which rivers flow." (48.5)

Sahih al-Bukhari Book 64, Hadith 214