but we have the ability of understanding which Allah may endow a person with, so that he may understand the Qur'an".
That's not a good English translation. If you know Arabic you would know that this is not a good translation of the Arabic:
أَوْ فَهْمٌ أُعْطِيَهُ رَجُلٌ مُسْلِمٌ، أَوْ مَا فِي هَذِهِ الصَّحِيفَةِ.
The suitable Arabic translation would be:
or the power of understanding which has been bestowed (by Allah) upon a Muslim
or what is (written) in this sheet of paper (with me).'
Seeing that this is the answer to the question "Have you got any book?'" then it becomes clear that it is not only the Qur'an.
Can you tell me where is that written paper or the contents of the written paper mentioned by Ali available in the world if it was actually a divine revelation? Ali would be contradicting his initial comment if the contents of the paper available with him were in fact divine revelation. And also even assuming what is written in the written paper were divine revelation, based on the hadith it would mean that it was only what were written on the paper that were divine revelations outside Quran. THINK.
Ali already said the contents (i.e. diyyah, ransom for captives, etc.) and we already know their rulings from other traditions.
There was no need for that document if everything was laid out in the Qur'an. That's the point.... Ali didn't only say "Qur'an" and stay quiet.
because the Quran was the only source of religious guidance for all muslims lived at that time.
There is no historical evidence to show that.
As a leader of the community, as a ruler, the prophet may have prohibited many bad practices, like Mut'a, prevailed in the soceity based on general directives contained in the Quran. It has nothing to do a revelation outside Quran.
And the donkey meat?
How about this tradition from Ali:
Narrated `Ali:
I heard the Prophet saying, "Mary, the daughter of `Imran, was the best among the women (of the world of her time) and Khadija is the best amongst the women. (of this nation). (Bukhari, Book 60, Hadith 103)
How would they know that Khadijah is the best amongst women in this nation in the sight of Allah without revelation in the Qur'an?
Musnad Ahmad narrates 804 narrations from Ali with many of them being authentic. I doubt you will accept if I show you ones that show that he didn't believe in Qur'an Onlyism.
Again, what's the point of your argument. You don't trust in the hadith system. So why are you trying to prove that Ali is on your side by appealing to the hadith? I don't think there is a need to proceed without first clarifying that point.