[The Soundest Chains of Transmission]
The first tier is the one that some leading scholars have described as comprising “the soundest isnāds,” yet the authoritative view is not to ascribe that label absolutely to any single chain in particular (1). Admittedly, when all the isnāds to which the scholars did apply that description are considered together (2), their collective weight shows them to be preferable to those chains that were not so designated (3).
[Comparing al-Bukhārī and Muslim]
A related question of preference (4)(5) concerns the material that both of the two Shaykhs—al-Bukhārī and Muslim—include, as against what is reported by only one of them, and likewise what al-Bukhārī alone narrates in relation to what Muslim alone narrates (6)(7). Because the scholars who came after them unanimously received both of their compilations with acceptance, while differing (8) over which of the two is weightier (9), whatever the two agree upon enjoys, from this standpoint, a stronger claim to authenticity (10) than that over which they did not concur (11).
The majority have stated explicitly that Ṣaḥīḥ al-Bukhārī is superior in overall soundness, and no one has been found to have asserted the opposite outright.