During Kaydar's governorship, al-Ma'mun ordered the beginning of the mihnah or inquisition, to ensure compliance with his belief that the Qur'an had been created. In 833 Kaydar received a letter from al-Ma'mun's brother and successor Abu Ishaq, announcing the formation of the mihnah and instructing him to implement it in Egypt. He accordingly questioned the qadi Harun ibn Abdallah al-Zuhri, along with other officials and legal experts, and received their affirmation of the createdness of the Qur'an.[4]