He was an able polemicist, firmly grounded in argument. He performed the pilgrimage in 317 AH, composed a refutation of al-Ṭaḥāwī on the question of nabīdh (fermented drink), then returned to the Maghrib and busied himself with his own pursuits; Qāḍī ʿIyāḍ records these details.

When Abū Yazīd Makhlad ibn Kindād al-Aʿraj, the leader of the Khārijites, rose up against the Banū ʿUbayd, this al-Mamsī joined him together with a number of the scholars of Qayrawān, so great was the tribulation that had befallen them. The ʿUbaydī ruler had now cast off all pretence and revealed what he had long concealed. They even stationed Ḥasan the Blind—an inveterate curser—along the roads, coaching him to chant rhymed invectives such as:

“Curse the Cave and all it holds,
and the Cloak and what it enfolds,”

and similar lines; anyone who objected was beheaded on the spot.

This took place at the dawn of the rule of the third, Ismāʿīl (1). Makhlad al-Zanātī, the ascetic famed for riding a she-donkey, thereupon marched out; his uprising stirred everyone, and he captured town after town, eventually seizing the city of Qayrawān. Yet the Khārijites perpetrated every sort of atrocity, until the scholars came to Abū Yazīd and reproached him. He retorted, “Plundering you is lawful for us!” They spoke to him gently until he ordered his men to desist, while the ʿUbaydī ruler barricaded himself in al-Mahdiyya.

It is also said that when Abū Yazīd felt certain of triumph, his Khārijite disposition overpowered him. He instructed his commanders, “If you meet the ʿUbaydī forces, withdraw from the people of Qayrawān so that their enemy may fall upon them.” They obeyed, and a great many were martyred; this occurred in the early 330s AH (2).

Thus the Khārijites are enemies of the Muslims, whereas the Bāṭinite ʿUbaydiyya are enemies of Allah and His Messenger.