Ar-Risala tul-Ghausia is very famous book of Syedna Ghaus ul Azam Shaikh Abdul Qadir Jilani in which he has described all his inspirational talking with Allah during the spiritual ascension which reveals secrets of Allah. Apparently this book looks quite small like a sum of few words but this is full of secrets of gnosis of Allah and it is kind of syllabus for the travellers of the path of truth. A brief exegesis of Al-Risala tul Ghausia is published which will be quite helpful for seeker to understand the path of Faqr.
