«Principles of islamic Jurisprudence» in 5 volumes, a work by It is considered one of the most important books of fundamentals in general, and the books of Hanbali principles in particular, as its author Bin Aqil al-Hanbali (benefited from what was in the book of his sheikh, Abu Ya`la al-Farra, and added to it much of his wealth of knowledge and extensive knowledge.