From Sahih Bukhari (Hadith 4170):
Narrated Al-Musaiyab: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)
Reference: Bukhari 4170