One day in the month of Rajab, Shaykh Abdul Qadir al-Jilani said: The Prophet s.a.w is reported as having said: "Wear out your devils by saying: 'There is no God but Allah; Muhammad is the Messenger of Allah. La ilaha illAllah Muhammadun Rasulullah', for the devil will be worn out by this, just as one of you may wear out his camel by riding it a lot and making it carry his burdens."
O my people! Wear out your devils by being sincere in saying: 'There is no god but Allah,' not merely with the words themselves. The affirmation of Unity (tawhid) burns devils both human and jinn, because it is fire (nar) to devils and light (nur) to those who affirm Unity (muwahhidun). How can you say: 'There is no god but Allah', when there is many a god (ilah) in your heart? Everything you rely upon and trust, apart from Allah, is your idol (sanam). It will do you no good to make the affirmation on Unity with your tongue, while at the same time being guilty of idolatry in your heart. You cannot benefit from purity of the outer form (qalab) accompanied by defilement of the heart (qalb). He who affirms Unity wears out his devil, but in the case of the idolater (mushrik) it is his devil that wears him out. Sincerity (ikhlas) is the kernel of words and deeds, because when they are empty of it they are a shell with no kernel. The shell is good for nothing but the fire.
The Sublime Revelation. A collection of sixty two discourses. Al-Fath ar-Rabbani Shaykh Abdul Qadir al-Jilani. Translated from the Arabic by Muhtar Holland.