If any action be either virtuous or vicious, it is only as a sign of some quality or character. It must depend upon durable principles of the mind, which extend over the whole conduct, and enter into the personal character. Actions themselves, not proceeding from any constant principle, have no influence on love or hatred, pride or humility; and consequently are never considered in morality.
This reflection is self-evident, and deserves to be attended to, as being of the utmost importance in the present subject. We are never to consider any single action in our enquiries concerning the origin of morals; but only the quality or character from which the action proceeded. These alone are durable enough to affect our sentiments concerning the person. Actions are, indeed, better indications of a character than words, or even wishes and sentiments; but it is only so far as they are such indications, that they are attended with love or hatred, praise or blame.
Hume, Treatise 22.214.171.124-5. A very strong claim, and when Hume makes a claim this strong, he means it seriously.