“Excellence is an art won by training and habituation: we do not act rightly because we have virtue or excellence, but we rather have these because we have acted rightly; 'these virtues are formed in man by his doing the actions'; we are what we repeatedly do. Excellence, then, is not an act but a habit: 'the good of man is a working of the soul in the way of excellence in a complete life... for as it is not one swallow or one fine day that makes a spring, so it is not one day or a short time that makes a man blessed and happy.'”

Variant: We are what we repeatedly do. Greatness then, is not an act, but a habit
Source: The Story of Philosophy (1926), p. 87. The quoted phrases within the quotation are from the Nicomachean Ethics, Book II, 4; Book I, 7.
Context: Excellence is an art won by training and habituation: we do not act rightly because we have virtue or excellence, but we rather have these because we have acted rightly; 'these virtues are formed in man by his doing the actions'; we are what we repeatedly do. Excellence, then, is not an act but a habit: 'the good of man is a working of the soul in the way of excellence in a complete life... for as it is not one swallow or one fine day that makes a spring, so it is not one day or a short time that makes a man blessed and happy'.

Knox to George Washington on when the cannon would arrive. Reported in David McCullough, 1776 (2005), p. 83.

On the assassination of John F. Kennedy
The Sixties, 1963 entry.
The Journals of John Cheever (1991)

Source: The Exorcist

On Actors and the Art of Acting (Leipzig: Bernhard Tauchnitz, 1875) p. 13

Source: Zen and the Art of Motorcycle Maintenance (1974), Ch. 29
Context: "What moves the Greek warrior to deeds of heroism," Kitto comments, "is not a sense of duty as we understand it—duty towards others: it is rather duty towards himself. He strives after that which we translate 'virtue' but is in Greek aretê, 'excellence' … we shall have much to say about aretê. It runs through Greek life."
There, Phædrus thinks, is a definition of Quality that had existed a thousand years before the dialecticians ever thought to put it to word-traps. Anyone who cannot understand this meaning without logical definiens and definendum and differentia is either lying or so out of touch with the common lot of humanity as to be unworthy of receiving any reply whatsoever.

Don Soderquist “ The Wal-Mart Way: The Inside Story of the Success of the World's Largest Company https://books.google.com/books?id=mIxwVLXdyjQC&lpg=PR9&dq=Don%20Soderquist&pg=PR9#v=onepage&q=Don%20Soderquist&f=false, Thomas Nelson, April 2005, p. 33.
On Striving for Excellence

Response when asked about feelings as first Pakistani acting-Chief Justice from a minority community, by Onkar Singh in Indian Rediff News interview (14 February 2006).