“The reward is in doing, but doing without expecting anything… doing unselfishly.”
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“Girls can do anything. We do do anything and we expect to be treated as equals.”
Quoted in David Barber, Helen Clark, new chief of UN Development Programme," https://archive.is/20131125142737/www.monstersandcritics.com/news/asiapacific/news/article_1467092.php/PROFILE_Helen_Clark_new_chief_of_UN_Development_Programme_"PROFILE: Asia-Pacific News (26 March 2006)

“My whole religion is this: do every duty, and expect no reward for it, either here or hereafter.”
Greek Exercises (1888), written two days after his sixteenth birthday.
Youth
Context: I should like to believe my people's religion, which was just what I could wish, but alas, it is impossible. I have really no religion, for my God, being a spirit shown merely by reason to exist, his properties utterly unknown, is no help to my life. I have not the parson's comfortable doctrine that every good action has its reward, and every sin is forgiven. My whole religion is this: do every duty, and expect no reward for it, either here or hereafter.

Vithal Gadgil in: Sanjoy Hazarika "Rival of Singh Becomes India Premier"
After extending support to Shekahr to form the government.

The Huffington Post - Diana: The Legacy (31 Aug 2012) http://www.huffingtonpost.com/david-allison/diana-the-legacy_b_1844945.html
Source: Messages from the Masters: Tapping into the Power of Love

“I feel that the greatest reward for doing is the opportunity to do more.”
On receiving Congressional Medal for Distinguished Civilian Achievement (23 April 1956); several variations of this personal motto are often quoted, including:
The reward for work well done is the opportunity to do more.
As quoted in 50 American Heroes Every Kid Should Meet! (2001) by Dennis Denenberg and Lorraine Roscoe, p. 99
I feel that the greatest reward for success is the opportunity to do more.