ʿUthmān al-Dārimī transmitted from Yaḥyā that he said, “He is reliable.”
Likewise, al-Nasāʾī and a number of other critics declared him reliable.
Alī ibn al-Madīnī said, “He is reliable in what he reports from recognised narrators, but I deem him weak in what he relates from unknown ones.”
I say: the weakness in fact lies with those narrators themselves; he would narrate from every sort of transmitter, and Sufyān al-Thawrī—despite his great standing—did the very same.
Alī ibn al-Ḥusayn ibn al-Junayd reported that Ibn Numayr said, “Marwān would gather teachers from the alleyways.”
Al-ʿIjlī said, “Reliable, firmly grounded, whenever he narrates from well-known men; but when he narrates from the unknown there is much to criticise, and the report is worthless.”
Abū Ḥātim said, “Truthful—his veracity is unquestioned—yet he frequently relates from obscure shaykhs.”
ʿAbbās al-Dūrī said, “I asked Yaḥyā ibn Maʿīn about a hadith of Marwān ibn Muʿāwiyah on the authority of ʿAlī ibn Abī al-Walīd. He replied, ‘That is ʿAlī ibn Ghurāb; by Allah, I have never seen anyone more artful at tadlīs than he is.’ (1)
Duḥaym and others said: He died suddenly in the year 193 AH, one day before the Day of Tarwiyyah.