He remained as governor throughout the reign of al-Amin however due to the Fourth Fitna, Later switched his allegiance to the rival al-Ma'mun[1] probably in 812.
In Mecca, Dawud ibn Isa reminded worshippers that al-Amin had destroyed Harun ar Rashid's succession pledges and led them in swearing allegiance to al-Mamun.
During the Siege of Baghdad in the Fourth Fitna, things were getting worse and Tahir ibn Husayn (al-Ma'mun's general) pushed into the city, al-Amin sought to negotiate safe passage out.
Tahir ibn Husayn reluctantly agreed on the condition that al-Amin turn over his scepter, seal and other insignia of the caliphal office.
Al-Tabari quotes Tahir's letter to the new Caliph al-Ma'mun informing him of al-Amin's capture and execution and the state of peace resulting in Baghdad.