Abu Hatim ibn Hibban al-Busti: I have not seen on the face of the earth anyone who memorizes the science of hadith and memorizes the words of the Companions and their additions as if all the hadiths were before his eyes except Muhammad ibn Ishaq ibn Khuzaymah, and once: He, may God have mercy on him, was one of the imams of the world in knowledge, understanding, memorization, collection, and deduction until he spoke in hadith with a chain of narration that we do not know of anyone else among the most trustworthy
Ibn Abi Hatim al-Razi: Trustworthy, Truthful
al-Daraqutni: An Imam of Hadith, unparalleled
al-Dhahabi: The Hafiz, the Authoritative, the Sheikh of Islam, the Imam of Imams