Ibn Sīrīn’s report describes a historical practice of distinguishing Ahl al-Sunnah from Ahl al-Bidaʿ when examining transmitters after the fitnah. The report’s general wording must be distinguished from the later technical analysis. In his earlier commentary on the Muqaddimah, al-Nawawī records the following positions.
1. He reports agreement that the narration of one whose innovation is judged by qualified scholarship to entail unbelief is not accepted. This does not authorize a verdict against a particular person based on a mere label or accusation.
2. On innovation not judged to entail unbelief, one position rejects such reports categorically, considering the fault in probity not removed by sincere interpretation.
3. Another accepts a narrator who does not consider lying permissible in support of his school, whether or not he actively advocates it. Al-Nawawī reports this as attributed to al-Shāfiʿī.
4. A third accepts the non-advocate but rejects the advocate of an innovation; al-Nawawī attributes it to many, perhaps most, scholars and calls it the fairest and soundest position.
The grounds concern the actual risk to truthful, accurate transmission, the nature of the innovation, and advocacy. Ibn Sīrīn’s words remain intact as the earlier historical testimony; assessment of any specific transmitter still demands evidence.