Sahih al-Bukhari — Merits of the Helpers in Madinah (Ansaar) — Hadith No: 3890
Translation
Narrated Jabir bin `Abdullah:I was present with my two maternal uncles at Al-`Aqaba (where the pledge of allegiance was given). (Ibn 'Uyaina said, "One of the two was Al-Bara' bin Marur)