He is asking about original copies of Saheeh al-Bukhaari and Saheeh Muslim!
Question

                There are some of the Shi‘ah who cast aspersions upon the authenticity of Saheeh al-Bukhaari and Saheeh Muslim. Their main argument is that there are no original copies of these two books in the handwriting of the authors (may Allah have mercy on them). The secondary argument is that some of the commentators on al-Bukhaari discussed the meaning of some hadeeths that are not in al-Bukhaari. I hope that you can give a complete answer and settle the matter.
Praise be to Allah.
    One of the most important things that the 
    educated Muslim, or the Muslim who is acquainted with the classical legacy, 
    should understand is that stirring up doubts is easy and is something that 
    anyone could do, to stir up doubts about anything, even about basic givens 
    and common-sense issues on which people base their rational thinking. The 
    matter may even go so far that some of those who got carried away with 
    doubts and specious arguments ended up denying their own existence, and 
    doubted everything around them, which led to them being admitted to mental 
    health clinics, because they drifted so far from common sense and sound 
    human nature. 

    This is how we deal with many so-called 
    specious arguments which are, in reality, nothing but illusions uttered by 
    some people who are causing us trouble at this time. This always compels us 
    to start from the very beginning in establishing principles of sound 
    rational thinking in various fields of knowledge and education. 

    What is mentioned in the question is one 
    such example. If what the questioner meant by “original copies” is 
    manuscripts that the author wrote in his own hand, then according what 
    rational thinking or logic can it be said that it is essential that the 
    original manuscripts be extant in order to accept that a particular book is 
    correctly attributed to its author?! How many books are there in the world, 
    since people learned how to write, that could meet this irrational 
    condition?! 

    In order to understand how irrational 
    those who stipulate that condition are, all you have to do is imagine that 
    one of them entered a venerable library or well-known publishing house or 
    international bookstore and said to the person in charge, I will not accept 
    the attribution of any books you have in this huge store unless you give me 
    the original manuscript, written by the author himself, so that I will be 
    certain that these books are soundly attributed to their authors! Doing this 
    would be ignoring all the customs and academic and legal requirements which 
    guarantee to us nowadays that the book is sound and that it will not be 
    claimed by anyone other than the author, such as requirements to register 
    books in the National Library, to get permission to publish, making books 
    well-known to critics and providing well-established evidence to that 
    effect, and other similar academic ways of proving such matters. 

    We know for certain that some of those who 
    specialise in producing specious arguments know deep down in their hearts 
    how foolish and silly are the things they suggest and say, but at the same 
    time they persist in saying it because they know that merely stating his 
    specious with regard to anything that exists will inevitably have some 
    influence on people’s hearts and minds. Hence whatever results he gets will 
    suffice him, even if he only manages to confuse a few people. What matters 
    to him is that he shuffles the cards and causes confusion with regard to 
    sound ways of thinking. 

    However, Saheeh al-Bukhaari was 
    heard by ninety thousand men from Imam al-Bukhaari himself (may Allah have 
    mercy on him), as was stated by one of his most famous students, namely 
    Muhammad ibn Yoosuf al-Farbari (d. 320 AH). See: Tareekh Baghdaad 
    (2/9); Tareekh al-Islam (7/375). Al-Farbari’s narration of Saheeh 
    al-Bukhaari was famous because he lived for a long time and was precise 
    in copying it out. He heard it from al-Bukhaari (may Allah have mercy on 
    him) over three years, then a number of trustworthy narrators learned it 
    from him, and from them this book became well-known. 

    Al-Mustamli (d. 376 AH) – one of those who 
    narrated it from Muhammad ibn Yoosuf al-Farbari – said: I copied the book of 
    al-Bukhaari from its original text that was with Ibn Yoosuf, and I saw that 
    he had not completed it yet; there were many blank pages there, including 
    some isnaads after which he had not written any hadeeths, and some hadeeths 
    for which he had not written any isnaads. So we tried to complete that.

    End quote. Narrated by al-Baaji in at-Ta‘deel 
    wa’t-Tajreeh (1/310) 

    The Saheeh was narrated from al-Farbari 
    by a number of trustworthy narrators, among the most famous of whom were the 
    following: 

    Al-Mustamli (d. 376 AH), whose name was 
    Ibraaheem ibn Ahmad

    Al-Hamawi Khateeb Sarkhas (d. 381 AH), 
    whose name was ‘Abdullah ibn Ahmad

    Abu’l-Haytham al-Kashmeehani (d. 389 AH), 
    whose name was Muhammad ibn Makki

    Abu ‘Ali ash-Shabwi, whose name was 
    Muhammad ibn ‘Umar

    Ibn as-Sakan al-Bazzaaz (d. 353 AH), whose 
    name was Sa‘eed ibn ‘Uthmaan

    Abu Zayd al-Mirwazi (d. 371 AH), whose 
    name was Muhammad ibn Ahmad

    Abu Ahmad al-Jarjaani (d. 373 AH), whose 
    name was Muhammad ibn Muhammad 

    Among the trustworthy students of al-Bukhaari 
    who heard his Saheeh directly from him and transmitted it to the 
    people with its isnaads in written form was the imam, hafiz, faqeeh and 
    qaadi, Abu Ishaaq Ibraaheem ibn Ma‘qil ibn al-Hajjaaj an-Nasafi (d. 295). 
    The copy of an- Nasafi was transmitted by Imam al-Khattaabi (may Allah have 
    mercy on him), as he said in his commentary A‘laam al-Hadeeth 
    (1/105): We heard most of this book from the narration of Ibraaheem ibn 
    Ma‘qil an- Nasafi. Khalaf ibn Muhammad al-Khayyaam told us: Ibraaheem ibn 
    Ma‘qil told us, from him. 

    This is the most famous way that the 
    scholars of hadith had: they would read their books to their students, or 
    their students would read their books to them. Then those books would become 
    well-known through the students and narrators, not through the original 
    manuscript of the author, which was one copy that he kept for himself. There 
    were no printing presses or publishing houses at that time; instead of 
    printing presses there was the narration of students with strong isnaads. 

    What would any researcher find more 
    authentic than the transmission of trustworthy narrators narrating from the 
    manuscripts that were read to (and checked with) the author himself and 
    approved by him, as they said concerning the copy of as-Saghaanni: He copied 
    it from the manuscript that was read to the author (may Allah have mercy on 
    him)”?

    See: Fayd al-Baari by al-Kashmiri. 

    If you want to ask about how old the 
    manuscripts that are extant today are, the Orientalist Manjana said in 
    Cambridge in 1936 CE that the oldest manuscript he had come across up to 
    that point was written in 370 AH, according to the narration of al-Mirwazi 
    from al-Farbari. See Tareekh at-Turaath by Fu’aad Sizkeen (1/228). 

    One of the most famous manuscripts of the 
    book that has come down to us in modern times is the copy of al-Haafiz Abu 
    ‘Ali as-Sadafi (d. 514 AH), which he copied from the manuscript written by 
    Muhammad ibn ‘Ali ibn Mahmoud, which was read to Abu Dharr (may Allah have 
    mercy on him) and has his writing on it too. It was kept by al-‘Allaamah at-Taahir 
    ibn ‘Ashoor, who borrowed it from the library of Tobruk in Libya. 

    There is also the copy of the imam and 
    hafiz Sharaf ad-Deen ‘Ali ibn Ahmad al-Yoonayni, who is known as al-Ba‘li 
    al-Hanbali (d. 701 AH). He checked it against the original copy that was 
    read to al-Haafiz Abu Dharr al-Harawi, and the original copy that was read 
    to al-Aseeli, and the original copy al-Haafiz Ibn ‘Asaakir, and the original 
    copy that was read to Abu’l-Waqt in the presence of the grammarian and 
    linguist Ibn Maalik, the author of al-Alfiyyah (d. 672 AH). 

    And so on… if we were to keep listing the 
    copies of as-Saheeh that are extant in the manuscript libraries of 
    the world, and how close they were to the time when as-Saheeh was 
    written, and the large numbers of those who copied and checked them, and how 
    trustworthy they were, and how they checked their copies against the 
    authoritative main copies, that would take a great deal of time. It is 
    sufficient for you to go to one of the libraries where manuscripts are kept 
    and ask about Saheeh al-Bukhaari; you will find hundreds of copies 
    with sound chains of transmission going back to Imam al-Bukhaari himself. 
    Al-Fihris ash-Shaamil lists 2327 locations in various libraries in which 
    there are manuscripts of this book.

    See: al-Fihris ash-Shaamil li’t-Turaath 
    al-‘Arabi al-Islami al-Makhtoot, al-Hadeeth an-Nabawi wa ‘Uloomuhu 
    (1/493-565). 

    With regard to Saheeh Muslim, it is 
    no less well-known and widespread than the Saheeh of Imam al-Bukhaari, 
    as Brockelmann said: Saheeh Muslim almost matches Saheeh al-Bukhaari 
    in the number of manuscripts and their presence in most libraries, as he 
    stated in The History of Arabic Literature (3/180) 

    It has many chains of transmission which 
    confirm that the book is soundly attributed to its author. The number of 
    such chains of transmission is almost unlimited, to such an extent that a 
    number of scholars wrote books just to discuss the chains of transmission of
    Saheeh Muslim; there are eight such books, one of the last of which 
    was the book by al-Kattaani (d. 1327 AH) entitled Juz’ Asaaneed 
    Saheeh Muslim. 

    Shaykh Mashhoor Hasan Salmaan said: 

    A group of people learned this book from 
    Muslim, one of the most famous of whom was Ibraaheem ibn Muhammad ibn 
    Sufyaan. He heard it from its author no less than three times, and he 
    checked it against the copy of his shaykh, Muslim. Muslim’s copy was very 
    precious and dear to him; he carried it with him to ar-Rayy and placed it 
    before Abu Zur‘ah ar-Raazi and Ibn Waarah looked at it. A number of scholars 
    learned it from Sufyaan; among them was al-Jaloodi. His copy was in 
    circulation among the students and some of them made a copy of it… Many of 
    these copies were very precise and were read to some prominent scholars and 
    checked against other manuscripts. Therefore the scholars used it as a 
    reference for research and discussion; they used to refer to it when dealing 
    with issues and problems. There are many manuscript copies of as-Saheeh 
    in libraries throughout the world, and hardly any library is without it. 
    These copies vary in the dates at which they were copied and they vary in 
    condition. 

    In the library of al-Qarawiyyeen in Fez up 
    till now there is a very precious copy of it; this is the copy of Ibn Khayr 
    al-Ishbeeli, which he checked many times (against other manuscripts); he 
    heard it read to him and he read it to other shaykhs, to such an extent that 
    it is regarded as the greatest extant manuscript of Saheeh Muslim 
    in North Africa. Written on it in the handwriting of Ibn Khayr is a note 
    stating that he checked it against three other original manuscripts of the 
    copy of al-Haafiz Abu ‘Ali al-Jiyaani. 

    End quote from al-Imam Muslim ibn al-Hajjaaj 
    wa Manhajuhu fi’s-Saheeh (1/375-376) 

    As for the claim that “some of the 
    commentators on al-Bukhaari discussed the meaning of some hadeeths that are 
    not in al-Bukhaari”, we have not found a single example of that. Differences 
    in the reports in Saheeh al-Bukhaari only occur in a few, very minor 
    cases having to do with the isnaads or some phrases in the texts, or the 
    chapter headings. But to suggest that there are some independent hadeeths 
    under some headings that were mentioned in some manuscripts but not others, 
    we could not find any example of that. 

    Even if we assume that they exist, it is 
    not something to object to or find strange. If the narrators who narrated 
    from the Prophet (blessings and peace of Allah be upon him) differed 
    sometimes, whereby some of the Sahaabah narrated the hadeeth with a 
    particular wording, and others narrated it with a different wording, or some 
    of the Sahaabah narrated a hadeeth and others did not remember it, in dozens 
    of examples, that does not undermine the principle of the Prophetic Sunnah, 
    and it does not shed doubt on the trustworthiness of the Sahaabah who 
    narrated from the Prophet (blessings and peace of Allah be upon him). So it 
    is more appropriate that the fact that there are slight differences between 
    the narrators of al-Jaami‘ as-Saheeh should not undermine the basic 
    authenticity of the book or its trustworthiness or its hadeeths and 
    reports. 

    We do not doubt that a lack of experience 
    in dealing with the classical Islamic legacy – and indeed a lack of 
    knowledge about the nature of history and manuscripts altogether – is the 
    reason for such misleading ideas or extreme ignorance and lack of 
    understanding on the part of the one who says that. 

    Otherwise, anyone who has any knowledge of 
    these branches of knowledge will be certain that minor differences in 
    reports or manuscripts in classical books is something natural in the light 
    of the fact that people in the past relied on copying by hand, and because 
    means of communication were very simple, and copyists were sometimes 
    imprecise in adhering to the original text; indeed they were sometimes 
    unaware of alterations that the author himself had introduced to his book 
    that would lead to some differences in the copies, as happened in the case 
    of Sunan at-Tirmidhi, Sunan Abi Dawood, al-Muwatta’ by 
    Imam Maalik, and the Musnad of Imam Ahmad ibn Hanbal. Indeed that 
    also happened in the case of the poetry of the Jaahiliyyah before that, and 
    in the books of Plato, Aristotle, and the entire legacy of Greek philosophy, 
    and in the case of both the Torah and the Gospel. 

    We hope that by giving these brief 
    highlights, readers will be alerted to the nature of these specious 
    arguments that are made and will realise that a little rational thinking, 
    with a little experience, will be sufficient to ward off all these specious 
    arguments. 

    See: Riwaayaat wa Nusakh al-Jaami‘ as-Saheeh 
    li’l-Imam Abu ‘Abdullah Muhammad ibn Ismaa‘eel al-Bukhaari: Diraasah wa 
    Tahleel, by Dr. Muhammad ibn ‘Abd al-Kareem ibn ‘Ubayd, which was of 
    great use to us in preparing the answer given above. 

    And Allah knows best.