There is a sort of gratification in doing good which makes us rejoice in ourselves, and a generous pride that accompanies a good conscience.

[Il y a certes je ne sçay quelle congratulation, de bien faire, qui nous resjouit en nous mesmes, et une fierté genereuse, qui accompagne la bonne conscience.]

Michel de Montaigne (1533-1592) French essayist

Essays, Book 3, ch. 2 “Of Repentence [Du repentir]” (1586) (3.2) (1595) [tr. Frame (1943)]
    (Source)

First appeared in the 1588 edition.

(Source (French)). Alternate translations:

There is truely I wot not what kinde of congratulation, of well doing, which rejoyceth us in our selves, and a generous jollitie, that accompanieth a good conscience.
[tr. Florio (1603)]

There is a kind of I know not what congratulation in well-doing, that gives us an inward Satisfaction, and a certain generous Boldness that accompanies a good Conscience.
[tr. Cotton (1686)]

There is a kind of, I know not what, congratulation in well-doing that gives us an inward satisfaction, and a generous boldness that accompanies a good conscience.
[tr. Cotton/Hazlitt (1877)]

There is surely I know not what self-gratification in doing well, which rejoices us ourselves, and a noble pride which attends a good conscience.
[tr. Ives (1925)]

There is an unutterable delight in acting well which makes us inwardly rejoice; a noble feeling of pride accompanies a good conscience.
[tr. Screech (1987)]