Arthur Schopenhauer, On the Basis of Morality (1839)

Boundless compassion for all living beings is the firmest and surest guarantee of pure moral conduct, and needs no casuistry. Whoever is inspired with it will assuredly injure no one, will wrong no one, will encroach on no one's rights; on the contrary, he will be lenient and patient with everyone, will forgive everyone, will help everyone as much as he can, and all his actions will bear the stamp of justice, philanthropy, and loving-kindness. On the other hand, if we attempt to say, "This man is virtuous but knows no compassion," or, "He is an unjust and malicious man yet he is very compassionate," the contradiction is obvious. Tastes differ, but I know of no finer prayer than the one which ends old Indian dramas (just as in former times English plays ended with a prayer for the King). It runs: "May all living beings remain free from pain."