We draw upon two major sources in order to acquaint ourselves with the Shari'ah of Muhammad (peace be upon him), viz. the Qur'an and the Hadith. The Qur'an is a divine revelation each and every word of the instructions issued or the memoirs of the last Prophet's conduct and behavior, as preserved by those who were present in his company or those to whom these were handed down by the first witness. These were later sifted and collected by divines and compiled in the form of books among which the collections made by Malik, Bukhari, Muslim, Tirmizi, Abu Dawud, Nasa'i and Ibn Majah are considered to be the most authentic.
FIQH
Detailed law derived from the Qur'an and the Ahadith covering the myriads from of problems that arise in the course of man's life have been compiled by some of the leading legists in the past. Thus, the Muslim Peoples shall forever be grateful to those men of leading and vision who devoted their lives to gaining a mastery of the Qur'an and the Hadith who made it easy for every Muslim to fashion his everyday affairs according to the requirements of the Shari'ah. It is due to them alone that the Muslims all over the world can follow the Shari'ah easily even though their attainments in religion are never such that they could themselves give a correct and authentic interpretation to the Qur'an or the Ahadith.
Though in the beginning a large number of religious leaders applied themselves to the task now only four major school of thought remain. They are:
Fiqh-e-Hanafi: This is the Fiqh compiled by Abu Hanifa Nu'man bin Thabit with the assistance and cooperation of Abu Yusuf, Muhammad, Zufar, and others all of whom had high religious attainments to their credit. This is known as the Hanafi School of Fiqh.
Fiqh-e-Maliki: This Fiqh was derived by Malik bin Anas Asbahi.
Fiqh-e-Shafi'i: Founded by Muhammad bin Idress al-Shafi'i.
Fiqh-e-Hanbali: Founded by Ahmed bin Hanbal.
All of these were given the final form within two hundred years of the time of the Prophet. The difference that appears in the four school are but the natural outcome of the fact that is many sided. When different persons employ themselves in interpreting a given event, they come out with explanations according to their own lights. What gives these various schools of thought the authenticity that is associated with them is the unimpeachable integrity of their respective founders and the authenticity of the method they adopted. That's why all Muslims, whatever school they may belong to regard all the four schools of Fiqh goes unchallenged, one can follow only one of them in one's life, though there is the group of Ahl-i-Hadith who believe that those who have the required knowledge and learning should directly approach the Qur'an and the Hadith for guidance and those who are not bestowed with such knowledge and faculties should follow whomsoever they may choose to in a particular matter.