Sayyiduna Salim bin Ubayd (may Allah be pleased with him), who was one of the People of the Suffah, said: Sayyiduna Abu Bakr (may Allah be pleased with him) was with the Prophet (peace and blessings be upon him). It was said: "O companion of the Prophet (peace and blessings be upon him)! Has the Prophet (peace and blessings be upon him) passed away?" He said: "Yes," and they came to know it. Then he said: "Leave your companion to his cousins," meaning for washing him. Then he came out, and the Muhajirun gathered and began consulting, and they said: "Let us go to our Ansari brothers; we will consult them as well, for they too have a right (in this)." They came to the Ansar, and a man of the Ansar said: "One leader from you and one from us." Sayyiduna Umar (may Allah be pleased with him) said: "Two swords in one sheath; this will not work." He took the hand of Sayyiduna Abu Bakr (may Allah be pleased with him) and asked: "About whom are these three verses: 'When the two were in the cave' [Surah al-Tawbah: 40], 'When he said to his companion' [Surah al-Tawbah: 40], and 'Do not grieve; indeed, Allah is with us' [Surah al-Tawbah: 40]?" Then Sayyiduna Umar (may Allah be pleased with him) spread out the hand of Sayyiduna Abu Bakr (may Allah be pleased with him), pledged allegiance and told the people as well, and the people pledged allegiance in the finest manner.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / 16549