This is a reference to some well-known formulas used in various religious sources of the early period of Islam (e.g., "I said, he said"). Hossein Modarressi employs this reference as an example of the use of reports that contain external evidence such as widespread language and style of legal discourse.
This source is part of the Online Companion to Hossein Modarressi, Text and Interpretation: Imam Jaʿfar al-Ṣādiq and His Legacy in Islamic Law (Harvard University Press, 2022).