“If you consume all your strength of time in worthless matters. And therefore, due to a lack of time and strength cannot work on what’s eternal, how regrettable that would be! You will regret forever.”

The Hypocrite Detected, Anatomized

Speech in West Calder, Scotland (27 November 1879), quoted in W. E. Gladstone, Midlothian Speeches 1879 (Leicester University Press, 1971), p. 116.
1870s
Context: My fourth principle is—that you should avoid needless and entangling engagements. You may boast about them, you may brag about them, you may say you are procuring consideration of the country. You may say that an Englishman may now hold up his head among the nations. But what does all this come to, gentlemen? It comes to this, that you are increasing your engagements without increasing your strength; and if you increase your engagements without increasing strength, you diminish strength, you abolish strength; you really reduce the empire and do not increase it. You render it less capable of performing its duties; you render it an inheritance less precious to hand on to future generations.

Sinngedichte I, 2, 58.

Larry Brantley – the heart (and voice) behind Wishbone! http://hollyfranklin.com/larrybrantley/ (September 17, 2016)

Source: No Logo: Taking Aim at the Brand Bullies 1999, Chapter One, "No Space"

This saying is not found in any source before 2010, when it was posted by The Ignorant Fisherman at Free Republic http://www.freerepublic.com/focus/bloggers/2451682/posts on 15 February. The language is not that of Washington or his time.
Misattributed, Spurious attributions

A Short History of Decay (1949)