This is a reference to a report from Jaʿfar al-Ṣādiq where he advises his followers to suspend judgment and refer the case to the Imam when they are unable to discern a legal ruling based on the sources.
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).