The Thirty-Second Category
Gharib al-Hadith (Unfamiliar Words in Hadith)
It is every obscure word that appears in the text of a hadith and is difficult to grasp because it is seldom used. This is a significant discipline, yet venturing into it is arduous, so whoever engages in it must exercise great care. The early generations were extremely meticulous in this regard. Scholars have authored many works on this science. It is said that the first to compile on the subject was al-Nadr ibn Shumayl; others claim it was Abu ʿUbaydah Maʿmar ibn al-Muthanna. After them came Abu ʿUbayd al-Qāsim ibn Sallām, who treated the material comprehensively and with excellence; then Ibn Qutaybah, who covered what had eluded Abu ʿUbayd; and finally al-Khattābī, who supplied what had escaped the two of them. These are its seminal works. Many later books contain additions and valuable points, yet one should rely only on those whose authors are eminent imams. The finest explanation is what has already been clarified within an authentic report itself. Allah knows best.

The Thirty-Third Category
Al-Musalsal (Serial Chains)
It is a hadith whose transmitters follow one another in sharing a particular attribute or condition—sometimes related to the narrators themselves, other times to the manner of narration. The attributes of narrators include words, actions, and many other kinds, such as the musalsal involving interlacing the fingers or counting with them, or the coincidence of the narrators’ names, epithets, or nisbas, for example reports we have received in which every transmitter was a Damascene, or the “musalsal of the jurists.” As for attributes of the narration, they include chains serially transmitted with the wording “I heard,” or “he informed us,” or “So-and-so informed us—by Allah.” The most meritorious type is the one that indicates an unbroken chain; among its benefits is heightened accuracy, yet it rarely remains free from some defect.