Sunan Ibn Majah, Chapter: The Chapters on Tribulations

"The Messenger of Allah (saw) stood up and addressed the people saying: 'No, by Allah, I do not fear for you, O people, but I fear the attractions of this world that Allah brings forth for you.' A man said to him: 'O Messenger of Allah(saw), does good bring forth evil?' The Messenger of Allah (saw) remained silent for a while, then he said: 'What did you say?' He said: 'I said, does good bring forth evil?' The Messenger of Allah (saw) said: 'Good does not bring forth anything but good, but is it really good? Everything that grows on the banks of a stream may either kill if overeaten or (at least) make the animals sick, except if an animal eats its fill of Khadir* and then faces the sun, and then defecates and urinates, chews the cud and then returns to graze again. Whoever takes wealth in a lawful manner, it will be blessed for him, but whoever takes it in an unlawful manner, his likeness is that of one who eats and it never satisfied.'"