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
← Previous Hadith I said to Salama bin Al-Akwa`, "For what did you give the Pledge of allegiance to Allah's Messenger (ﷺ) on the day of Al-Hudaibiya?" He replied, "For death (in the Cause of Islam.).

Sahih al-Bukhari Book 64, Hadith 211 Next Hadith → 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