those which al-Bukhārī and Muslim both include, and those which each of them transmits independently of the other.

In al-Mizzī’s Tahdhīb al-Kamāl and the books that branch out from it, one also finds narrators who are not represented at all in the Six Books. They are recorded only to differentiate them from earlier namesakes who do have narrations in those collections, and they are flagged with the word tamyīz (distinction) beside the entry.

Take, for instance, the heading “Kathir ibn Abī Kathir.” Five individuals appear under this name: the first is cited by Abū Dāwūd, al-Tirmidhī, al-Nasāʾī, and Ibn Mājah in their tafsīr chapters; the second is mentioned by al-Bukhārī in al-Adab al-Mufrad; the remaining three have no narrations at all and are listed solely to distinguish them from the first two.

Abū Naṣr al-Kalābādhī produced a separate compilation of the transmitters found in Ṣaḥīḥ al-Bukhārī, while Abū Bakr ibn Manjūyah al-Iṣfahānī did the same for those in Ṣaḥīḥ Muslim.