 Muhammad also wrote to the tax officials throughout the empire, instructing them that their revenues were to be sent to Baghdad instead of Samarra.For his part, al-Mu'tazz wrote to Muhammad, urging him to declare allegiance to him.Soon after, al-Mu'tazz put his brother Abu Ahmad (the later al-Muwaffaq) in command of an army and instructed him to fight against al-Musta'in and Muhammad.