“4537. The Fool is busy in everyone's Business but his own.”

Reported in Hoyt's New Cyclopedia Of Practical Quotations (1922), p. 86. The quotation has been attributed to many others, such as Lord Chief Justice Campbell, Lord Chesterfield, Sir William Harcourt, Lord Pembroke, Lord Westbury, and to an anonymous judge, and said to have been spoken in court to Garter King at Arms, Rouge Dragon Pursuivant, or some other high-ranking herald, who had confused a "bend" with a "bar" or had demanded fees to which he was not entitled. George Bernard Shaw quotes it in Pygmalion (1912) in the form, "The silly people dont [sic] know their own silly business."

Maule cannot be the original source of the quotation, as it is quoted nearly twenty years before his birth in Charles Jenner's The Placid Man: Or, The Memoirs of Sir Charles Beville (1770): "Sir Harry Clayton ... was perhaps far better qualified to have written a Peerage of England than Garter King at Arms, or Rouge Dragon, or any of those parti-coloured officers of the court of honor, who, as a great man complained on a late solemnity, are but too often so silly as not to know their own silly business." "Old Lord Pembroke" (Henry Herbert, 9th Earl of Pembroke) is said by Horace Walpole (in a letter of May 28, 1774 to the Rev. William Cole) to have directed the quip, "Thou silly fellow! Thou dost not know thy own silly business," at John Anstis, Garter King at Arms (though in his 1833 edition of Walpole's letters to Sir Horace Mann, George Agar-Ellis, 1st Baron Dover, attributes the saying to Lord Chesterfield in a footnote, in the form "You foolish man, you do not understand your own foolish business"). Edmund Burke also quotes it ("'Silly man, that dost not know thy own silly trade!' was once well said: but the trade here is not silly.") in a "Speech in the Impeachment of Warren Hastings, Esq." on May 7, 1789 (when Maule was just over a year old). Chesterfield or Pembroke fit best in point of time.
Attributed

Source: Howl's Moving Castle

Section 10
The True Believer (1951), Part One: The Appeal of Mass Movements

The Better Part (1901)
Context: I AM an Anarchist.
All good men are Anarchists.
All cultured, kindly men; all gentlemen; all just men are Anarchists.
Jesus was an Anarchist.
A Monarchist is one who believes a monarch should govern. A Plutocrat believes in the rule of the rich. A Democrat holds that the majority should dictate. An Aristocrat thinks only the wise should decide; while an Anarchist does not believe in government at all. Richard Croker is a Monarchist; Mark Hanna a Plutocrat; Cleveland a Democrat; Cabot Lodge an Aristocrat; William Penn, Henry D. Thoreau, Bronson Alcott and Walt Whitman were Anarchists. An Anarchist is one who minds his own business. An Anarchist does not believe in sending warships across wide oceans to kill brown men, and lay waste rice fields, and burn the homes of people who are fighting for liberty. An Anarchist does not drive women with babes at their breasts and other women with babes unborn, children and old men into the jungle to be devoured by beasts or fever or fear, or die of hunger, homeless, unhouseled and undone.
Destruction, violence, ravages, murder, are perpetrated by statute law..

Source: Don Quixote de la Mancha (1605–1615), Part I, Book III, Ch. 8.

Source: The Gate to Women's Country (1988), Chapter 16 (p. 173)

Though at times attributed to Leary on the internet, no published source of this has been located. It is a misquote of a William S. Burroughs reading entitled M.O.B. from the Giorno Poetry Systems boxed set. M.O.B. was an extension of Burroughs' expression in The Place of Dead Roads (1983), p. 155:
You are a Shit Spotter. It's satisfying work. … We have observed that most of the trouble in the world has been caused by ten to twenty percent of folks who can't mind their own business, because they have no business of their own to mind, any more than a smallpox virus … The mark of a basic shit is that he has to be right.
Misattributed

Peter de Noronha, The Pageant of Life (1964), Pages 134-135,
The Pageant of Life (1964), Businessmen

Source: Dreams of Steel (1990), Chapter 29 (p. 331)