This is a study of an early Hanafī jurist, Īsā b. Aban (d. 221/836). After collecting historical information about his life, I explore his views, as preserved in a fourth-century text, al-Fusūl fī'l-Usūl by Abū Bakr al-Jassās. Īsā's views, as presented there, shed important light on the development of the Hanafī concept of prophetic reports. I refer to non-Hanafī texts in order to check any possible ideological reconstruction by Jassās. Finally I compare my findings with J. Schacht's observations on 'early schools of law' and find interesting parallels between them and Īsā's views, as presented by Jassās.