This category of ḥasan narration shares (1) with the ṣaḥīḥ grade (2) the capacity to serve as authoritative evidence—even though it ranks beneath it—and it likewise resembles it (3) in being subdivided into tiers, some higher than others.
[The ṣaḥīḥ derived from external corroboration]
“It is deemed sound when its routes are many,” and it is only ruled (4) ṣaḥīḥ once the chains have multiplied, for the composite picture (5) possesses a strength (6) that makes up for the degree to which the precision of a ḥasan narrator falls short of that of a ṣaḥīḥ narrator. Accordingly, the term ṣaḥīḥ is applied to an isnād that, had it stood alone, would have been ḥasan li-dhātihi, once it has multiple supporting lines (7). This applies when a single descriptor (8) is used.
[Explaining how one ḥadīth can be called both ḥasan and ṣaḥīḥ]
If the two qualifiers—ṣaḥīḥ and ḥasan—are combined (9) in a single description (10), as in al-Tirmidhī’s and others’ wording (11), “a ḥadīth that is ḥasan ṣaḥīḥ,”
(1) MS H reads: “musharikin” (genitive, with tanwin), while MS Y has: “yusharik.” The adopted reading is that of MSS D and K.
(2) MSS A and Y read: “al-sahih.”
(3) MS H has: “wa-mushabihin” (genitive, with tanwin); the accepted wording follows MSS B, D, W, H, Y, and K.
(4) MS W reads: “nahkum”; in MSS A and H the word is written without the requisite dotting.
(5) MS B has: “li-l-darura,” its margin notes: “li-l-turuq,” and MS T reads: “al-sura.”
(6) MS B reads: “quwwatun” (nominative, with tanwin); the adopted form follows MSS A, D, W, H, Y, K, and M.
(7) MS A has: “infarada.”
(8) MSS A and H read: “yatafarrad.”
(9) MS A reads: “al-hasan wa-sahih,” reversing the usual order.
(10) MS L has: “wasfi hadithin wahidin,” and MS D: “wasfi wahidin” (in genitive construction); the accepted wording follows MSS A, B, W, Z, and K. Al-Laqani, in Qada al-Watr (p. 782), comments: “(Fi wasfi wahidin): it should be read as a genitive phrase, i.e., fi wasfi hadithin wahidin. Some copies indeed have it so. One may also say that, since both adjectives qualify a single noun, they were treated as though they formed a single description.”
(11) Examples include Yaqub ibn Shaybah and Abu Ali al-Tusi. See: al-Taqyid wa-l-Idah by al-Iraqi, p. 52; al-Nukat by the author, 1/429; Hashiyat Ibn Qutlubagha, p. 60.