Wa alaikum assalam
In my humble view, the argument would present itself as thus:
- The Quran does not authorise any other source for religious guidance for believers [1]. The burden of proof is with others to prove otherwise, not with you. [2]
- There is no mention of 'Hazrat Uthman' in the Quran or who was specifically involved in the Quran's compilation. Such stories are found in Ahadith sources canonised centuries later by fallible men. The Quran provides its own testimony as to its compilation. It was arguably, fully canonised and transmitted (both orally and in written form) en masse in the life of the prophet. [3]
- The Quran is clear guidance and other than its language [Note 1], requires no other source for interpretation / or religious interpretation [4]
- Even if the Ahadith corpus could be proven 100% authentic it is irrelevant as the question is of 'authority' – not authenticity. The Quran provides no authority for another source for religious guidance for believers. Of course, the sources that it does ratify, such as aspects of the previous scriptures are mentioned in the Quran. [5], [6], [7].
I hope this helps, God willing,
Regards,
Joseph
REFERENCES:[1] THE QURAN STANDS ALONE AS SOLE RELIGIOUS GUIDANCEhttp://quransmessage.com/articles/quran%20sole%20guidance%20FM3.htm
[2] BURDEN OF PROOF - PROPHET ABRAHAM'S (pbuh) ARGUMENThttp://quransmessage.com/articles/burdenofproof%20FM3.htm
[3] THE COMPILATION OF THE QURANhttp://quransmessage.com/articles/the%20compilation%20of%20the%20quran%20FM3.htm
[4] GOD HAS WARNED BELIEVERS TO ONLY FOLLOW THE QURANhttp://quransmessage.com/articles/god%20has%20warned%20believers%20to%20only%20follow%20the%20quran%20FM3.htm
[5] 'BETWEEN HIS HANDS' OR 'BEFORE IT' (MA BAYNA YADAYHI)http://quransmessage.com/articles/between%20hands%20or%20before%20it%20FM3.htm
[6] The TWO GUIDES - THE QURAN AND THE BIBLEhttps://www.facebook.com/joseph.a.islam/posts/300599863410481
[7] LAMBASTING THE BIBLEhttp://quransmessage.com/forum/index.php?topic=146
[NOTE 1]: PRESERVATION OF THE LANGUAGEThe protection of the 'dhikr' (reminder) is assured by the Quran (15:9). This implies both the 'words' of the Quran and an appropriate ability to discern its 'meanings'. Otherwise, the 'dhikr' would be meaningless.
Therefore any source, including classical lexicons, works of grammarians, dictionaries or indeed, any Islamic secondary source as defined above which is used to understand the classical Arabic language is implicitly ratified by the Quran (15:9).
The Prophet was tasked with a responsibility to convey the message of the Quran in Arabic to his people. His people had a responsibility en masse to pass the message to mankind (22:78) both in Arabic and to convey its meaning to those who did not understand the language
Source: http://quransmessage.com/articles/hadith%20FM2.htm