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.The brothers had different mothers. Al-Amin was prompted to move against al-Ma'mun by meddlesome ministers, especially al-Fadl ibn al-Rabi'. Al-Amin had Harun's succession documents brought from Mecca to Baghdad, where he destroyed them. Al-Amin sent agents east to stir opposition to al-Ma'mun. However, a careful watch at the frontier denied these the opportunity. Al-Amin denied al-Ma'mun's request for his family and money and kept them in Baghdad.In March 811 Al-Amin dispatched an army under Ali ibn Isa ibn Mahan against Al-Ma'mun. Ali advanced on Rayy. Ma'mun's capable general Tahir bin Husain met and defeated Ali, who was killed.