“O disciple, how many nights have you spent rehearsing your learning, reading books, and depriving yourself of sleep? I do not know what the motive was in this? If it was winning the goods of the world, the allure of its vanities, receiving its honors, and competing in glory among your peers, then woe to you and woe again! But if your objective was the revival of the Prophet’s law, the cultivation of your character and breaking the soul that incites evil, then blessing upon you and blessing again!
O disciple, live as long as you want, but you must die. Love whatever you desire, you will become separated from it. Do whatever you wish; you will be repaid for it.
Know that the unrestrained tongue, and the heart that is rusted over and full of negligence and greed, are a sign of misfortune. If you do not kill the ego with sincere exertion, your heart will not be animated by the lights of knowledge.
O disciple, knowledge without action is madness and action without knowledge is void. Know that the knowledge which does not remove you from sins today and does not convert you to obedience, will not remove you tomorrow from hellfire. If you do not act according to your knowledge today and you do not make amends for days gone by, you will say tomorrow, ‘send me back and I will act virtuously!’ And it will be replied, ‘Fool! You have just come from there.’.”
Abu Hamid Al-Ghazali (1058-1111) – from Letter to a Disciple