Muslim’s Criterion for Inclusion:
Al-Nawawi, in the introduction to his commentary on Ṣaḥīḥ Muslim, cites Ibn al-Ṣalāḥ who said: “Muslim—may Allah have mercy on him—stipulated for the hadiths in his Ṣaḥīḥ that the chain of transmission be uninterrupted, each link narrated by a trustworthy transmitter from another trustworthy transmitter, from beginning to end, free of any irregularity or hidden defect.”
Al-Ḥāfiẓ Ibn Ḥajar, while listing the various ranks of authentic reports in his commentary on Nukhbat al-Fikar, adds: “Priority, in terms of superior authenticity, is then given to what fulfills the joint criterion of both Imams, for by their criterion we mean the narrators approved by them together with the remaining conditions of soundness.”
From the introduction to his Ṣaḥīḥ it is evident that Muslim divides the narrations into three categories:
- Those transmitted by master-memorizers of proven precision.
- Those transmitted by upright narrators of average accuracy and retention.
- Those transmitted by weak or abandoned narrators.
After completing the first category he follows it with the second, whereas the third he ignores entirely. He also states at the close of his introduction that, when a narrator transmits by ʿanʿana (using the word “from”), it is sufficient that he be a contemporary of the person from whom he reports, provided he is not known for tadlīs (concealing an intermediary).