Nahjul Balagha Part 2, Letters and Sayings

Letter 68: To Salman al-Farisi before Amir al-mu'minin's caliphate

Now, the example of the world is like that of a snake which is soft in touch but whose poison is fatal. Therefore, keep yourself aloof from whatever appears good to you because of its short stay with you. Do not worry for it because of your conviction that it will leave you and that its circumstances are vicissitudes. When you feel most attracted towards it, shun it most, because whenever someone is assured of happiness in it, it throws him into danger; or when he feels secure in it, the world alters his security into fear; and that is an end to the matter.