The source also cites a report in support of consensus:
«لا يجمع الله هذه الأمة على ضلالة أبداً»
Allah will never unite this community upon misguidance.
The author uses this as transmitted support for the proposition that an authoritative, established agreement of the community does not rest on error.
Methodological caution: citing a report in a textbook and independently evaluating its chains are different matters. This lesson explains the source’s legal argument; it does not purport to assess every transmission route or hadith grading.