Al-Ma'mun had distrusted al-Amin before their father's death and convinced Harun to take him with him on Harun's last journey east. Although Harun had instructed the Baghdad commanders of this expedition to remain with al-Ma'mun, after Harun's death they returned to Baghdad. Al-Amin sought to turn al-Ma'mun's financial agent in Rayy against al-Ma'mun and he ordered al-Ma'mun to acknowledge al-Amin's son Musa as heir and return to Baghdad. Al-Ma'mun replaced his agent in Rayy and refused the orders. His mother was Persian and he had strong support in Iran.