George Bernard Shaw citations

Life levels all men: death reveals the eminent.
en
Man And Superman, 1903

He who gives money he has not earned is generous with other people's labor.
en
Man And Superman, 1903

Beware of the man whose God is in the skies.
en
Man And Superman, 1903

He who can, does. He who can't, teaches.
en
Man And Superman, 1903

Do not do unto others as you would that they should do unto you. Their tastes may not be the same.
en
Man And Superman, 1903

A thing nobody believes cannot be proven too often.
en
Plays Unpleasant, 1931

The art of government is the organization of idolatry.
en
Man And Superman, 1903

There are fifty ways of saying Yes, and five hundred of saying No, but only one way of writing them down.
en
Plays Unpleasant, 1931

The reasonable man adapts himself to the world: the unreasonable one persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man.
en
Man And Superman, 1903

The bureaucracy consists of functionaries; the aristocracy, of idols; the democracy, of idolaters.
en
Man And Superman, 1903

Variante: Life isn't about finding yourself. Life is about creating yourself.

#124
1900s, Maxims for Revolutionists (1903)
Source: Man and Superman

Preface
1910s, The Doctor's Dilemma (1911)
Variante: A life spent making mistakes is not only more honorable but more useful than a life spent doing nothing.
Contexte: Attention and activity lead to mistakes as well as to successes; but a life spent in making mistakes is not only more honorable but more useful than a life spent doing nothing.

Act II
Source: 1900s, John Bull's Other Island (1907)

The Serpent, in Pt. I, Act I
1920s, Back to Methuselah (1921)
Contexte: Everything is possible: everything. Listen. I am old. I am the old serpent, older than Adam, older than Eve. I remember Lilith, who came before Adam and Eve. I was her darling as I am yours. She was alone: there was no man with her. She saw death as you saw it when the fawn fell; and she knew then that she must find out how to renew herself and cast the skin like me. She had a mighty will: she strove and strove and willed and willed for more moons than there are leaves on all the trees of the garden. Her pangs were terrible: her groans drove sleep from Eden. She said it must never be again: that the burden of renewing life was past bearing: that it was too much for one. And when she cast the skin, lo! there was not one new Lilith but two: one like herself, the other like Adam. You were the one: Adam was the other.

Jesus, as portrayed in Preface, Difference Between Reader And Spectator
1930s, On the Rocks (1933)
Contexte: The kingdom of God is striving to come. The empire that looks back in terror shall give way to the kingdom that looks forward with hope. Terror drives men mad: hope and faith give them divine wisdom. The men whom you fill with fear will stick at no evil and perish in their sin: the men whom I fill with faith shall inherit the earth. I say to you Cast out fear. Speak no more vain things to me about the greatness of Rome. … You, standing for Rome, are the universal coward: I, standing for the kingdom of God, have braved everything, lost everything, and won an eternal crown.

#25
1900s, Maxims for Revolutionists (1903)
Source: Man and Superman

#1
1900s, Maxims for Revolutionists (1903)

Act III
Source: 1900s, Major Barbara (1905)

Source: Pygmalion & My Fair Lady

Source: Pygmalion

The Intelligent Woman's Guide to Socialism and Capitalism, Chapter 8 http://books.google.com/books?id=ys13gZliXFAC (1928)
1920s

The Two Pioneers
1890s, Quintessence Of Ibsenism (1891; 1913)

Saint Joan : A Chronicle Play In Six Scenes And An Epilogue (1923)
1920s

#17
1900s, Maxims for Revolutionists (1903)

Credited to Shaw in the lead in to the mockumentary C.S.A.: The Confederate States of America (2004) and other recent works, but this or slight variants of it are also sometimes attributed to W. C. Fields, Charlie Chaplin, and Oscar Wilde. It might possibly be derived from Shaw's statement in John Bull's Other Island (1907): "My way of joking is to tell the truth. It's the funniest joke in the world."
Another possibility is that it is derived from Shaw's characteristic of Mark Twain: "He has to put things in such a way as to make people who would otherwise hang him believe he is joking."
Variants:
If you are going to tell people the truth, you'd better make them laugh. Otherwise, they'll kill you.
If you're going to tell people the truth, you'd better make them laugh. Otherwise, they'll kill you.
Disputed

Everybody's Political What's What? (ebook, must be borrowed) https://openlibrary.org/books/OL24979564M/Everybody's_political_what's_what (1944), Chapter XXXVII: Creed and Conduct, p. 330
1940s and later
Variante: Progress is impossible without change; and those who cannot change their minds cannot change anything.
Contexte: Progress is impossible without change; and those who cannot change their minds cannot change anything. Creeds, articles, and institutes of religious faith ossify our brains and make change impossible. As such they are nuisances, and in practice have to be mostly ignored.

Source: Man and Superman

Variante: If you cannot get rid of the family skeleton, you may as well make it dance.
Source: Immaturity

Source: 1900s, Man and Superman (1903), p. 23