Majma al-Zawaid — Hadith 9018

Rafi' al-Ta'i, who was with Sayyiduna Abu Bakr (may Allah be pleased with him) in the expedition of Dhat al-Salasil, said: I asked him about what had been said concerning their pledge of allegiance. He began to tell what position the Ansar had taken, what he had discussed with them, what Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) had discussed with the Ansar in this regard, and how he had reminded them of my leading them in prayer by the command of the Prophet (peace and blessings be upon him) during his illness (that I should lead the prayer). So the Ansar pledged allegiance to me on that account, and I accepted that pledge from them, because I feared that a trial might come, after which there would be apostasy.
Ahmad recorded it from his teacher Ali bin Ayyash, whom I do not know; the rest of its narrators are thiqat (trustworthy).