It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the flag of the Prophet (peace and blessings be upon him) for the Muhajirun used to be with Sayyiduna Ali (may Allah be pleased with him), and for the Ansar it used to be with Sayyiduna Sa’d bin Ubadah (may Allah be pleased with him), and when the battle would intensify, the Prophet (peace and blessings be upon him) would be under the flag of the Ansar.