As-Saheehayn confirmed authentic based on Muslims' continuous transmission
24-2-2015 | IslamWeb
Question:
I have read the response u gave me regarding this question but I am not satisfied!....So I am asking again!...please answer my question with proofs, may Allah reward you! Can you provide me with the references and sources from which it can be said that two sahihain(bukhari & muslim) are authentic i.e.,that the two Imams took utmost care to compile these ahadith?...What are the sources from which we can say that these books are still in the original preserved form(without additions or deletions) that they were written by Imam Bukhari & Muslim?
Answer:
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
In our Fataawa 21893, 83766, 85547, 86172, 87578 and 185295, we mentioned statements from the scholars about the authenticity of the Ahaadeeth presented in As-Saheehayn (the two Saheeh books) of Al-Bukhari and Muslim and about the privileged status of these two works. We did not mention the references in the previous answer because we did not find any of them translated into English. You are advised to consult reliable scholars in the Islamic Centers in your country; they may refer you to some translated references, if any exist.
As for the evidence that As-Saheehayn of Al-Bukhari and Muslim are decisively attributed to Imaams Al-Bukhari and Muslim 
and that they remain in their forms without alterations or distortions, it is simply because the Muslim community at large has preserved the Ahaadeeth in these two books throughout the ages and until this very day. Those who preserve them cite them on the authority of their teachers with a continuous chain of narration. Hadeeth scholars continue to hold study groups for reciting from memory the Hadeeth books in general, and the As-Saheehayn of Al-Bukhari and Muslim in particular. Indeed, this is an actualization of the divine promise of preserving the Sunnah of the Prophet, sallallaahu ‘alayhi wa sallam. Allaah The Exalted says (what means): {Indeed, it is We who sent down the revelation and indeed, We will be its guardian.} [Quran 15:9] Undoubtedly, the Sunnah of the Prophet, sallallaahu ‘alayhi wa sallam, is part of the divine revelation as evidenced by the Quran; Allaah The Exalted says (what means): {Nor does he speak from [his own] inclination.* It is not but a revelation revealed.} [Quran 53:3-4] He also says (what means): {[We sent them] with clear proofs and written ordinances. And We revealed to you the message that you may make clear to the people what was sent down to them and that they might give thought.} [Quran 16:44]
Allaah has honored the Muslim community with many special characteristics that were not given to any other community. From among those favors is the Isnaad (chain of narration) in the various sciences of Islamic knowledge. The Isnaad was regarded by the early Muslim generations as a fundamental condition in relating any aspect of the religion. ‘Abdullaah ibn Al-Mubaarak 
said: "Verily, the Isnaad is part of the religion; and if it were not for the Isnaad, anyone could say whatever he wishes to say."
Allaah Knows best.