Al-Ḥāfidh al-Dhahabī said:

And he wrote, read and corrected (works) and also excelled in the sciences related to the narrations and the Sunan. He studied, gave verdict, made tafsīr and authored the most amazing of works. He was alone in holding certain opinions and as a result his honour was attacked, yet he is a man who has sins and mistakes. Despite this, and by Allāh, my eyes have not seen the likes of him and he has not seen the likes of himself. He was a skilled and erudite Imām in the various sciences related to the religion, had a correct and sound mind, extremely quick in his perception, fluent in his understanding, overflowing with good deeds and was characterized by excessive braveness and generosity. He kept away from the desires of food, clothing and sexual relations. He did not find pleasure in anything but the spreading of knowledge, putting it into books and then acting upon its requirements. Abū Fatḥ al-Yaʿmarī mentioned him in answering the questions of Abū al-ʿAbbās bin Dimyāṭī al-Ḥāfidh, saying, "I found him to be amongst those who had acquired a fortune of knowledge and he fully and completely memorise the Sunan and the Āthār. If he spoke about tafsīr then he would be the carrier of its flag or if the gave a legal ruling in fiqh, he would know its extreme depths. And if he was to recall a hadīth he would possess all the knowledge related to it and would carry its flag (make the ḥadīth take precedence over all else). And if he was to talk about the various religions and factions, no one who was more vast in knowledge or greater in meticulousness could be seen. He surpassed his contemporaries in every science and my eyes have not seen the likes of him and nor have his eyes seen the likes of himself." I (adh-Dhahabī) say: He was imprisoned on more than one occasion in order that he would slacken with respect to his antagonists and so that the fluency of his tongue and pen may diminish. Yet he would not recant and nor turn around upon the advice of anyone, up until he died while imprisoned at the Damascus Prison on the 20th of Dhu al-Qaʿdah, in the year 728H. And his followers consisted of nations, (the like of) their number could not be found at the graves of the Sūfīs, may Allāh forgive him and have mercy upon him, āmīn.

In Muʿjam al-Muḥaddithīn (p. 25), through al-Kawkab al-Durrī. And it is also cited by Ibn Rajab al-Ḥanbalī in Dhayl Ṭabaqāt al-Ḥānābilah (4/499-500).

From the forthcoming publication, "The Creed of the Early Kullabi Ash'aris."