What is the ruling on breaking an oath of allegiance?

It is not permissible to break the pledge of allegiance (bay'ah) to the Imam unless there is clear disbelief (kufr bawāḥ). Whoever breaks it dies a death of ignorance (mītat Jāhiliyyah). A severe warning has been issued against whoever pledges allegiance to the Imam for worldly gain and then breaks the pledge if they do not achieve what they desire. This is the belief of Ahl al-Sunnah.