Why was Muhammad Ahmad al-Mahdi expelled by his Sufi teacher?

Muhammad Ahmad al-Mahdi was expelled by his shaykh (teacher) because of his highly emotional and intransigent religious observance. Specifically, al-Mahdi had begun to reprove his teacher for worldliness, which exasperated the shaykh and led to his expulsion from the circle of disciples. Following this, al-Mahdi unsuccessfully sought his teacher's pardon before joining the brotherhood of a rival shaykh within the same order.1