"Do what thou wilt shall be the whole of the Law."
Dictated to Crowley in Cairo between noon and 1:00p.m. on three successive days in April 1904, The Book of the Law is the source book and key for Crowley students and for the occult in general.
The holy text that forms the basis of Crowley's belief system, Thelema, was transmitted to him by the entity known as Aiwass over the course of three fateful April days in 1904.
With his wife Rose as the medium for what would become known as the Cairo Working, Crowley dutifully transcribed the communications on hotel stationery.
The pamphlet has since passed into occult legend.
Its full title is Liber AL vel Legis, sub figura CCXX, as delivered by XCIII=418 to DCLXVI, and it is commonly referred to as The Book of the Law.
Although the "messenger" of AL was Aiwass, Aiwass presents the Book as an expression of three god-forms of the three chapters, Nuit, Hadit, and Ra-Hoor-Khuit.