The Islamic book referred to in the crossword solution is the KORAN, which is the central religious text of Islam. It is believed to be the word of God as revealed to the Prophet Muhammad and is composed of 114 chapters known as surahs. The KORAN is divided into sections that deal with various aspects of life, including faith, morality, and law. It is considered to be the most important source of guidance for Muslims and is widely studied and memorized.