Sufyān, Mālik, Ḥammād ibn Zayd, and Ibn al-Mubārak.

It is also related from Ibn Mahdī that he said, “I have never seen a man more knowledgeable in hadith than Sufyān, more sound-minded than Mālik, more austere than Shuʿbah, or more sincere toward the ummah than Ibn al-Mubārak.”

Muḥammad ibn al-Muthannā reports: I heard ʿAbd al-Raḥmān ibn Mahdī say, “My eyes have never beheld the like of four men: I have not seen anyone with a stronger retention of hadith than ath-Thawrī, anyone more rigorous in self-denial than Shuʿbah, anyone more intelligent than Mālik, or anyone more sincerely devoted to the welfare of the ummah than Ibn al-Mubārak.” (1)

Abū Nashīṭ relates: I heard Nuʿaym ibn Ḥammād say, “I asked Ibn Mahdī, ‘Which of the two is superior, Ibn al-Mubārak or Sufyān ath-Thawrī?’ He replied, ‘Ibn al-Mubārak.’ I said, ‘People disagree with you.’ He responded, ‘They have never tested him; I have never seen the like of Ibn al-Mubārak.’” (2)

Nūḥ ibn Ḥabīb narrates: Ibn Mahdī told us, “Ibn al-Mubārak narrated to us, and he was one of a kind—peerless.” (3)

Aḥmad ibn Muḥammad ibn al-Qāsim ibn Muḥriz says: I heard Yaḥyā ibn Maʿīn remark, “I heard Ibn Mahdī declare, ‘Ibn al-Mubārak is more knowledgeable than Sufyān ath-Thawrī.’” (4)

Muḥammad ibn Aʿyan relates: I heard ʿAbd al-Raḥmān ibn Mahdī while the hadith scholars were gathered around him. They asked, “You sat with ath-Thawrī and heard from him, and you heard from Ibn al-Mubārak as well; which of the two carries greater weight?” He answered, “Even if Sufyān exerted himself to be like ʿAbd Allāh (Ibn al-Mubārak) for a single day, he would not be able to.” (5)