All that is included in Usul (the science of principles of...

All that is included in Usul (the science of principles of obtaining religious rules) books as sources of Ijtihad are: (1) Allah’s Book—the Holy Qur’an, (2) The Holy Prophet’s Sunnah (tradition) and the tradition of the and the , (3) Ijma’ (consensus), (4) Aql (wisdom), (5) Qiyas (analogy), (6) Istihsan (approbation) and (7) Masalih Mursalah .

In the following discussion, we review the above sources and their proof[^28] briefly to see which of them can be used as the religious reasons to obtain the rules. Examining the proof of the Holy Qur’an Among the mentioned sources, all Muslims agree upon the proof of the Holy Qur’an. Of course, some Sunni books like Sahih Al-Bukhari [^29] and Sahih Muslim [^30] and some Shi’a ones such as Al-Kafi [^31] include traditions stating that some Qur’anic Verses have not survived to be available to us.