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Some of the Mujasima have latched onto the opinion of Ibn Al-Salah, who believed that reports found in Sahih Bukhari and Sahih Muslim are all decisively reliable (Qat’iat Al-Thubut). Ibn Al-Salah‘s reasoning: there is consensus (Ijma’) on the reliability of the two books, so all of the singular reports contained within are decisively reliable by virtue of this consensus.
Know that the above is a weak opinion, which most scholars disagree with. Imam Al-Nawawi’s response to Ibn Al-Salah’s position is recorded in Al-Suyuti’s Tadrib Al-Rawi (pg. 142):
| Al-Nawawi said: And most scholars disagreed with Ibn Al-Salah, saying: “a report is indecisive as long as it is not mass transmitted”.
And he [Al-Nawawi] said in his commentary of Sahih Muslim: Such is the state of the singular narration. And it makes no difference whether it is reported by the two sheikhs [Bukhari and Muslim] or anyone else. The Ummah’s acceptance of the two Sahihs is only proof that we do not need to check the authenticity of their reports before acting upon them. This is unlike narrations found in other books, which need to be scrutinized and authenticated first. But just because the Ummah has agreed to act upon those narrations, doesn’t mean that they have agreed that the narrations are decisively the words of the Prophet ﷺ. |
Comment: and the claim that there is consensus with regards to the authenticity of all reports in the two Sahihs, is a claim that should be subjected to further study.
Keys to the Unseen 
Assalamu alaikum, what if one claims that the meanings of the sunnah are preserved, so that once the hadith can be shown to be authentic, it becomes decisively reliable at that point?
Wa ‘Alaykum Al-Salam,
Many meanings from the Sunnah are decisively reliable (i.e. Qati’at Al-Thubut). And this is given multiple singular narrations that support those meanings. But the decisiveness of this meaning would not be by virtue of the decisiveness of any single report, since each of those reports is indecisively reliable (i.e. Dhani Al-Thubut). Rather, the meaning is decisive because the reports, when taken collectively, decisively establish that meaning. And what is true of one part of a composite, is not necessarily true of the composite as a whole. You will find more on that here.
To give an example: you might receive a report concerning a country you’ve never visited- let’s say Japan for example. That single report is indecisively reliable. In that, you would not be justified in believing with certainty that Japan exists, by virtue of this one report on its own. But when that single report is coupled with another, and then another, and then another, and so on and so forth, from multiple independent witnesses, this collection of reports is altogether decisive proof for the existence of Japan. So the existence of Japan is decisively established by virtue of the collection of reports informing you of its existence, not by virtue of any one of those reports.
In the same way: you have many narrations reporting the battle of Badr for example. Each of those narrations is indecisively reliable. But when those narrations are taken altogether, they are collectively decisive proof for the battle of Badr. Hence, we are certain that the battle of Badr occurred, by virtue of the collection of narrations reporting its occurrence, even though each single report in this collection is indecisively reliable.