No man is absolutely indifferent to the happiness and misery of others.
 David Hume, An Enquiry Concerning the Principles of Morals (1751). copy citation

Context

“It is sufficient, that this is experienced to be a principle in human nature. We must stop somewhere in our examination of causes; and there are, in every science, some general principles, beyond which we cannot hope to find any principle more general. No man is absolutely indifferent to the happiness and misery of others. The first has a natural tendency to give pleasure; the second, pain. This every one may find in himself. It is not probable, that these principles can be resolved into principles more simple and universal, whatever attempts may have been made to that purpose.” source