DawudTalut
Peace be upon you.
And the evidence that Muhammad's Qur'an was the same as Abu Bakr's Qur'an which was the same as Uthman's Qur'an (barring some minor variations)?
Almost all Companions were alive by the time of Hazrat Abu Bakr (may Allah be pleased with him). Had there been any variation, they would have said so, and same continues at natural pace onward :
"....in the time of the Holy Prophet himself the Quran used to be recorded in writing, was committed to memory and was constantly recited and thousands of people knew the whole of it by heart,...."
"Abu Bakr.......... appointed Zaid bin Thabit, being one of those who used to record the Quran at the dictation of the Holy Prophet, to collect the text of the Quran in one volume and appointed prominent Companions of the Holy Prophet to assist him in the task. Abu Bakr directed that the text of the Quran should be collected from its recorded fragments and that the accuracy of the text should be certified by two persons who knew the whole of the Quran by heart. This task was soon accomplished and a written text of the whole of the Quran was got together in one volume, which was certified as accurate by those who knew it by heart."
"He [Uthman] had copies prepared of the text which had been collected in the time of Abu Bakr..."
"In the time of the Holy Prophet the social life of the Arabs was based upon their tribal divisions ; each tribe led an existence separate from and independent of the others. In their speech they were accustomed to pronounce certain words in accordance with their own practice. When they accepted Islam they were welded into one cultured society and Arabic at once became the vehicle of that culture. Literacy spread very rapidly among the Arabs and it became quite easy for every one of them to adopt the correct literary enunciation of every Arabic word. The language of Mecca became the standard for this purpose. By the time of 'Uthman, therefore, no justification had been left for variations in the enunciation of vowel points in accordance with tribal practices in the recitation of the Quran, particularly when such variations were likely to lead to misconception in the minds of non-Arabs. 'Uthman's very prudent and timely action has been made the basis of the charge by nonMuslim writers that he made changes in the Quran or that the copies of the Quran promulgated by him were in some manner different from the standard text or the text as revealed to the Holy Prophet. These authors imagine that they have discovered a potent weapon of attack against the accuracy of the text of the Quran, but those who are acquainted with the Arabic language and with the history of the compilation of the Quran merely smile at the lack of intelligence betrayed by them. There can thus be no room for doubt that the text of the Quran promulgated by 'Uthman was exactly the same as that revealed to the Holy Prophet. There is still less room for doubt that the text of the Quran has continued absolutely pure and uncorrupted since 'Uthman had despatched copies of the standard text to different parts of the Muslim dominions. These copies were in turn multiplied so extensively and rapidly that very soon almost every literate Muslim possessed his own copy of the Quran. It is recorded that a few years later during the struggle between 'Ali and Mu'awiya the soldiers of the latter's army on one occasion tied copies of the Quran to the points of their lances and proclaimed that the Quran should decide between the two opposing factions (The Caliphate). This shows that by that time it was usual for every Muslim to possess his own copy."
Ref: https://www.alislam.org/library/books/Introduction-Study-Holy-Quran.pdf
Unique Divine Promise for Holy Quran
[ch15:v10] Verily, We Ourself have sent down this Exhortation, and most surely We will be its Guardian.