Part I, CH 2: Chamberlain, p. 32
The Killer Angels (1974)
“Don't do the right thing looking for a reward, because it might not come.”
In a 2004 interview with AP. http://www.nytimes.com/2006/01/07/national/07thompson.html
Attributed
Help us to complete the source, original and additional information
Hugh Thompson, Jr. 11
United States helicopter pilot during the Vietnam War 1943–2006Related quotes

“I do not wish any reward but to know I have done the right thing.”
Source: The Adventures of Huckleberry Finn

“Happiness is a reward that comes to those that have not looked for it.”
Victories
Alain On Happiness (1928)
“Don't worry about it. The right thing will come at the right time.”
Source: Until the End of Time
Criticising European food safety laws; as quoted in City AM, Fri 15 Feb 2013 p. 23

We The Living (1936)
Source: We The Living Part One Chapter 6