Asbab-al-Nuzul or occasions and circumstances for the revelations; refers to a field of study and genre of literature devoted to recounting the circumstances of the Prophet Muhammad and his followers when particular verses from the Qur'an were revealed. Legal scholars regard this study as of great importance, on the principle that sound understanding of the revelation proceeds from knowing the reasons Allah revealed the Qur'an and how the Prophet Muhammad applied the revelation when he received it. Asbab al-Nuzul sheds light on the ayah, it enlightens the tafsir and application of the ayah. The earliest and the most important work in this genre is undoubtedly Kitab Asbab al-Nuzul (Book of Occasions and Circumstances of revelation) of Ali ibn Ahmad al-Wahidi. Al-Wahidi mentions occasions of about 570 verses out of 6236 verses of the Qur'an. Wahidi's work is not only the first attempt to collect all the material regarding the occasions of revelation in one single volume, but it is also the standard upon which all subsequent works were based.