The Max Planck Encyclopedia of Public International Law (MPEPIL) online edition, edited by Rüdiger Wolfrum, is a fully updated online edition of the Encyclopedia of Public International Law published in print between 1991 and 2001 under the general editorship of Rudolf Bernhardt.
Relevant Chapters include the following:
Islamic Approach to International Law
International Law, Regional Developments: Islam
Organization of the Islamic Conference (OIC)