Allah's Apostle said, "The thing I am afraid of most for your sake, is the worldly blessings which Allah will bring forth to you." It was said, "What are the blessings of this world?" The Prophet said, "The pleasures of the world." A man said, "Can the good bring forth evil?" The Prophet kept quiet for a while till we thought that he was being inspired divinely. Then he started removing the sweat from his forehead and said, "Where is the questioner?" That man said, "I (am present)." Abu Sa'id added: We thanked the man when the result (of his question) was such. The Prophet said, "Good never brings forth but good. This wealth (of the world) is (like) green and sweet (fruit), and all the vegetation which grows on the bank of a stream either kills or nearly kills the animal that eats too much of it, except the animal that eats the Khadira (a kind of vegetation). Such an animal eats till its stomach is full and then it faces the sun and starts ruminating and then it passes out dung and urine and goes to eat again. This worldly wealth is (like) sweet (fruit), and if a person earns it (the wealth) in a legal way and spends it properly, then it is an excellent helper, and whoever earns it in an illegal way, he will be like the one who eats but is never satisfied."

Sahih Bukhari