This is a reference to how Mālik b. Anas (the eponym of the Mālikī school of law) remembered Jaʿfar al-Ṣādiq: exceptional in his manners and religious devotion.
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).