Abu Ali al-Asbahani al-Haddad: Among the narrators, I have never seen anyone with a stronger memory than Abu Umar. Due to his vast memorization, he was accused of lying. He would be asked about something that the questioner thought he had made up, and he would answer it. Then, someone else would ask him the same question a year later, and he would give the exact same answer.
Al-Khatib al-Baghdadi: All of our Sheikhs considered him trustworthy and truthful.
Al-Dhahabi: He has a section on the virtues of Muawiyah, in which there are many fabricated hadiths, and the fault in them lies with someone other than him.
Abd al-Wahid ibn Burhan: I saw our Sheikhs consider him trustworthy and believe him in hadith.
Ubayd Allah ibn Ahmad al-Azhari: He accused him.
Ubayd Allah ibn Ahmad al-Sirfi: As for the hadith, we saw all our Sheikhs consider him trustworthy and truthful in it.
Muhammad ibn Ishaq al-Nadim: A group of scholars considered him weak, and he was the ultimate in hypocrisy.