"Qawaid al-Tasawwuf is one of the works of Ahmad Zarruq that all biographers list among his most important. Zarruq himself gives his reasons for undertaking this work in its opening pages as: '. . .to introduce the principles and foundations of Sufism in a manner that integrates the Sacred Law with the Truth, and links the principles of religion and jurisprudence with the Path.' Zarruq’s purpose in this is not to prove Sufism’s orthodoxy to its critics, but to maintain Sufism’s integrity by using the criterion of the Law to expose dangerous perversions of practice... ... He would evaluate every Sufi position and practice, weighing them all in the balance of the Law of God. Kannun states that religious scholars after Zarruq, even to this day, have referred to him as 'the monitor of scholars and saints' (muhtasib al-'ulama wa al-awliya'). He continues: 'This is a grand and majestic attribute with which no Muslim scholar before or after him has been qualified.' Qawaid al-Tasawwuf is a monitor’s handbook. Because of its unwavering demand that practices reflect principles, the work can be considered an ethical guideline for Sufi aspirants, and has been so used for centuries within the Shadhili Order. Zarruq quotes the sayings of well-known shaykhs who preceded him, as well as his own teachers. But as often as he quotes Sufi shaykhs (many of whom are Shadhili), he relies upon the sayings of the great masters of jurisprudence (especially the Malikis). Zarruq shows that he is a master of both, and that both are necessary to the student." (Zaineb Istrabadi, The Principles of Sufism: "Introduction")