Western Analysis on how hadith became important source of law in Islam

The below quotation taken from Rueben Levy (1969). The Social Structure of Islam. Cambridge University Press. It is a good book on the social aspect of Muslim life in the past before the dominance or advance of western politics in the Muslim lands. It has some explanation on the theoretical aspect of Islamic law that has relevance to the practice of Muslim societies and states. Such an explanation is not new to the western academic and the reproduction below is a rendering how Sunna or Hadith becomes important source of law marginalizing the use of reason.

"The holy cities of Arabia, in which the memory of the Prophet Muhammad (s.a.w.) had been perpetuated by numerous account - some authentic, others certainly not so - covering all the incidents of his career. Especially at Medina, where he spent the latter and more influential period of his life, the part played by "tradition" in justifying local custom was important one. The learned of Medina, in fact, being compelled by circumstances to supplement the legal provisions of the Koran, did so not as the provincial Muslims had done, by an avowed resort to reason, but by deliberately inventing Hadiths of the Prophet to justify their new regulations or fresh ways of applying Koranic laws... The Hadith properly speaking, is the report of the Prophet's Sunna or course of conduct, or of his doings and sayings, to anyone of which a particular Hadith may refer. The obvious way out of the dilemmas provided by the Koran or by the need for reconciling Koranic doctrine with conflicting but ineradicable alien practice, was to refer to what the Prophet had done in similar circumstances, and consequently the Sunna acquired an authority only a little less than that of the Koran itself."   at page 170.