Abu Hatim al-Razi: The wonder of his mastery and freedom from error with what he was granted of memorization, and he once said: An Imam from the Imams of the Muslims
Abu Hatim ibn Habban al-Busti: He was one of the leaders of his time in jurisprudence, knowledge and memorization
Abu Dawud al-Sijistani: He changed five months before he died
Abu Zur’a al-Razi: No one was seen to have memorized more than Ishaq
Abu Yahya Muhammad ibn Yahya al-Sha’rani: I never saw a book in Ishaq's hand, and he never narrated except from memory
Ahmad ibn Hanbal: Someone like Ishaq is being asked about? Ishaq is an Imam from the Imams of the Muslims, and once: If Abu Yaqub, the Emir of the Believers, narrates to you, then adhere to it
Ahmad ibn Sa’id ibn Ibrahim: If al-Thawri, Ibn Uyainah and al-Humaydani were alive, they would need him
Ahmad ibn Shu’ayb al-Nasai: One of the Imams, and once: Trustworthy, reliable
Ibn Hajar al-Asqalani: Trustworthy Hadith Scholar, a student of Ahmad ibn Hanbal
Al-Dhahabi: The Imam of Khurasan
Al-Mizzi: One of the Imams of the Muslims and scholars of the religion, he combined knowledge of Hadith, jurisprudence, memorization, truthfulness, piety and asceticism
Zakariya ibn Dawud al-Khaffaf: He dictated to us eleven thousand Hadiths from his memory, then he read them and did not increase or decrease a letter
Sa’id ibn Dhu’ayb al-Marwazi: I do not know anyone on the face of the earth like Ishaq
Abd al-Latif ibn Ibrahim ibn al-Kayyal al-Shafi’i: An Imam from the flags of the Imams
Qutaybah ibn Sa’id: Imam
Muhammad ibn Aslam al-Tusi: I do not know anyone who was more fearful of Allah than Ishaq, and he was the most knowledgeable of the people, and if Sufyan al-Thawri were alive, he would need Ishaq
Muhammad ibn Ishaq ibn Khuzaymah: By Allah, if Ishaq ibn Ibrahim al-Hanthalee were among the Successors, they would have acknowledged his memorization, knowledge and jurisprudence
Yahya ibn Ma’in: He revived the Sunnah in the land of the East