Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) narrates: The Prophet (peace and blessings be upon him) sent Sayyiduna Khalid bin al-Walid (may Allah be pleased with him) and Sayyiduna Ali bin Abi Talib (may Allah be pleased with him) to Yemen. He appointed Sayyiduna Ali bin Abi Talib (may Allah be pleased with him) as commander over the Muhajirun and Sayyiduna Khalid bin al-Walid (may Allah be pleased with him) as commander over the Bedouins. He said: "If there is fighting, then Ali bin Abi Talib will be the commander over all the people."
Al-Tabarani recorded it. Its chain contains a narrator, Ibrahim bin Uthman Abu Shaybah, who is da'if (weak).