ibn Mūsā, who narrated to him from Ismāʿīl ibn Abī Khālid; likewise Abū Nuʿaym, who transmitted to him from al-Aʿmash; likewise Khallād ibn Yaḥyā, who related to him from ʿĪsā ibn Ṭuhmān; and ʿAlī ibn ʿAyyāsh together with ʿIṣām ibn Khālid, both of whom reported to him from Ḥarīz ibn ʿUthmān—the shaykhs of all these men being Successors.
The second tier consists of those who lived in the time of the foregoing authorities but did not hear from reliable Successors, such as Ādam ibn Abī Iyās, Abū Mushir ʿAbd al-Aʿlā ibn Mushir, Saʿīd ibn Abī Maryam, Ayyūb ibn Sulaymān ibn Bilāl, and their peers.
The third tier is the middle stratum of his teachers: men who did not meet the Successors but were leading figures of the next generation (the followers of the followers), such as Sulaymān ibn Ḥarb, Qutaybah ibn Saʿīd, Nuʿaym ibn Ḥammād, ʿAlī ibn al-Madīnī, Yaḥyā ibn Maʿīn, Aḥmad ibn Ḥanbal, Isḥāq ibn Rāhawayh, and Abū Bakr and ʿUthmān ibn Abī Shaybah, together with others of comparable rank. Muslim shared the privilege of transmitting from this tier.
The fourth tier comprises his companions in the pursuit of knowledge and those only slightly senior to him in audition, such as Muḥammad ibn Yaḥyā al-Dhuhlī, Abū Ḥātim al-Rāzī, Muḥammad ibn ʿAbd al-Raḥīm Sāʿiqah, ʿAbd ibn Ḥumayd, Aḥmad ibn al-Naḍr, and a group of their counterparts. From these he narrates only what he missed from his own teachers or could not obtain through anyone else.
The fifth tier is made up of people who, in both age and chain of transmission, were counted among his own students; he heard from them merely for supplementary benefit—such as ʿAbd Allāh ibn Ḥammād al-Āmulī, ʿAbd Allāh ibn Abī al-ʿĀṣ al-Khuwārizmī, Ḥusayn ibn Muḥammad al-Qabbānī, and others. He reported only a small number of narrations from them, acting on the maxim transmitted by ʿUthmān ibn Abī Shaybah from Wakīʿ: “A man is not a scholar until he relates from someone above him, someone equal to him, and someone below him.” Al-Bukhārī likewise said, “A ḥadīth-scholar is not complete until he writes from someone above him, someone equal to him, and someone below him.”