the two liars.(1) Reported by Muslim.(2)
[The Abandoned and the Munkar]
The second category of rejected reports—those set aside because the narrator is suspected of fabrication—is the matrūk (abandoned report).
The third is the munkar, according to those who do not require the additional element of contradiction for a report to be labelled munkar.
The same applies(3) to the fourth and fifth categories: anyone whose mistakes are egregious, whose heedlessness is frequent,(4) or whose open impiety is manifest—his ḥadith is deemed munkar.
Next comes error (wahm), which is the sixth category—mentioned explicitly(5) only because of the length of this discussion. If that error is established by corroborating evidence(6)—such as connecting what is actually mursal or munqaṭiʿ, merging one ḥadith into another, or the like(7) of these critical flaws—the report is rejected.
[The Defective Report]
Knowledge of such matters(8) is attained through extensive investigation and the collection of the various chains; this(9) is the muʿallal (report with a concealed defect), one of the most intricate disciplines within ḥadith science.