827 he proclaimed his belief in a central Mu'tazilite tenet, that the Qur'an had been created. By the end of al-Ma'mun's reign in 833, Ibn Abi Du'ad had become a close associate of the caliph, and on his deathbed al-Ma'mun recommended to his brother and successor al-Mu'tasim that he admit Ibn Abi Du'ad to his circle of advisors. Chief judge under al-Mu'tasim Following the accession of al-Mu'tasim, the new caliph followed his brother's advice by appointing Ibn Abi Du'ad as chief judge, replacing the latter's erstwhile patron Yahya ibn Aktham. During al-Mu'tasim's reign (r. 833–842), Ibn Abi Du'ad wielded enormous political and economic influence, and the caliph was said to be completely under his power, with neither his public or private business done without his advice. He became one of the senior officials of the state, although he was forced to contend with the vizier Muhammad ibn al-Zayyat, who became his chief rival in the administration. During the reign of al-Mu'tasim, Mu'tazilism was maintained as the official creed of the state. Although the caliph reportedly lacked al-Ma'mun's personal zeal for Mu'tazilism, he nevertheless continued his brother's religious policies, allegedly due to the influence of Ibn Abi Du'ad. To ensure compliance with the doctrine of the created Qur'an, the chief judge continued the Inquisition or . Initiated by al-Ma'mun just four months before his death, the required officials, judges and scholars to be tested on their beliefs regarding the nature of the Qur'an; individuals who refused to adhere to the position that it had been created were subject to dismissal, arrest or torture. Among the victims of the during this period was Ahmad ibn Hanbal, the founder of the Hanbali school of jurisprudence, who was tried by Ibn Abi Du'ad and flogged for maintaining his orthodox beliefs. Ibn Abi Du'ad also oversaw the appointment of several like-minded qadis to various cities throughout the empire, who similarly prosecuted the within their respective jurisdictions. Outside of his overseeing of the , Ibn Abi Du'ad spent his time at court developing a reputation for moderation and compassion, interceding on several occasions to save individuals who had become subject to al-Mu'tasim's wrath from punishment and securing favors from the caliph for various patrons. At the same time, he came to play an important role in the fiscal affairs of the caliphate, his staff overseeing, for example, the division of spoils during the Amorium campaign in