Immanuel Kant,
The Metaphysical Elements of Ethics
“ But in the imperative, which commands the duty of virtue, there is added, besides the notion of self-constraint, that of an end; not one that we have, but that we ought to have, which, therefore, pure practical reason has in itself, whose highest, unconditional end (which, however, continues to be duty) consists in this: that virtue is its own end and, by deserving well of men, is also its own reward. Herein it shines so brightly as an ideal to human perceptions, it seems to cast in the shade even holiness itself, which is never tempted to transgression. ”
