Most people thinking about Islam only consider three possible views on how to understand Reason:

1 - There is a harmony between revelation and reason (Ibn Rushd/Mu'tazilite)

2 - Reason is important but does not provide all the answers and requires oversight by revelation (Ghazali/Ashari)

3 - Reason is overrated and revelation is best understood by way of Love (Rumi/Sufi)

But there is a fourth strain that Islam has produced and we need to acknowledge it because there have been, are, and will be Muslims who will adopt this view:

Since reason is our most precious gift from Allah, we should do nothing to reduce its status or degrade it. Since reason should govern our conduct, we should allow nothing to govern it. Since reason is the sovereign over all human facilities, it should not be made subject to any other faculty.

Razi, from Kitab al Muluki h/t 2000 AH

In other words, his position is of pure rationalism. He remains a very important but extremely marginalized thinker within Islamic History. It reveals quite a lot about the intellectual climates that today most Muslims barely regard him as Muslim whereas a thousand years ago he was studying under one of the foremost authorities on the Quran (Tabari, whose exegesis of the Quran is still authoritative).

By the way, Razi also discovered coffee (as well as anesthesia), and you'll note that despite being a pure rationalist he was quite steeped in ethical theory, which rebuts the primary Ashari argument against pure rationalists (namely, that if you give primacy to reason you do not have morals):

It is thought that the great Persian philosopher-physician Razi (ca. 800 AD) might have been the first scholar to mention the plant, calling it bunchum. Razi is most famous for discovering that, if you get someone drunk enough, you can perform minor surgery on him with a minimum of fuss. Actually Razi was an immensely important scientist whose contributions to modern medicine cannot be overestimated, his work far outstripping that of his European contemporaries; he penned the first systematic works on allergies and immunology, on pharmaceutical equipment and tinctures, and on the menstrual cycle, among many other topics. In fact, after reviewing his achievements, I furiously wonder why it is that our modern doctors take a Hippocratic Oath and not a Razi Oath. Razi was also one of the earliest proponents of objective ethics in the practice of medicine.