This is a reference to the extent to which fabricators went to portray the Shīʿī Imams quoting the Sunna of the Prophet from some of his Family's archenemies. Hossein Modarressi cites this reference in his discussion of some of the features of al-Ṣādiq's views on ḥadīth fabrication.
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).