Abu Bakr al-Bayhaqi: Narrated the saying of Muhammad ibn Idris al-Shafi'i, that he is trustworthy
Abu Ja'far al-Basti: Trustworthy, and he has a better memory than al-Thaqafi
Abu Dawud al-Sijistani: There is no one among the narrators of hadith except that he has erred, except Isma'il ibn 'Ulya, and Bishr ibn al-Mufaddal
Abu 'Abd Allah al-Hakim al-Naysaburi: Among the trustworthy
Ahmad ibn Hanbal: The ultimate authority in verification in Basra
Ahmad ibn Shu'ayb al-Nasa'i: Trustworthy and Firm
Ibn Hajar al-'Asqalani: Trustworthy and Preserver
Al-Dhahabi: Imam, Authoritative Hadith Scholar
Shu'ba ibn al-Hajjaj: The Delight of the Jurists, and once: Master of the Hadith Scholars
Abd al-Rahman ibn Mahdi: Trustworthy and he said once: Ibn 'Ulya is more reliable than Hasheem and once: More reliable than a mirage
Uthman ibn Abi Shayba al-'Absi: Ibn 'Ulya is more reliable than the Banu Hashim, and I do not prefer anyone over him from the people of Basra
Ali ibn al-Madini: I would not say that anyone is more reliable in hadith than Ibn 'Ulya
Muhammad ibn Ja'far al-Ghandar: I was born into hadith the day I was born, and there is no one who is preferred in hadith over Isma'il ibn 'Ulya
Muhammad ibn Sa'd, the scribe of al-Waqidi: Trustworthy and Firm in hadith, an authority
Yahya ibn Sa'id al-Qattan: Ibn 'Ulya is more reliable than Wuhayb
Yahya ibn Ma'in: Trustworthy, Reliable, Truthful, Muslim, Pious, God-Fearing, and in the narration of Ibn Mahriz: He counted him among the trustworthy of Basra, Upright in hadith, he never wrote a single letter from Ayyub until after Ayyub died, meaning that he memorized it while he was alive
Ya'qub ibn Shayba al-Sudosi: Very firm