“There is some self-interest behind every friendship. There is no friendship without self-interests. This is a bitter truth.”

Ce que les hommes ont nommé amitié n'est qu'une société, qu'un ménagement réciproque d'intérêts, et qu'un échange de bons offices; ce n'est enfin qu'un commerce où l'amour-propre se propose toujours quelque chose à gagner.
Maxim 83.
Reflections; or Sentences and Moral Maxims (1665–1678)

Source: The Forge of God (1987), Chapter 52 (p. 352)

Former Dean of Islamic Law at Qatar University Abd Al-Hamid Al-Ansari: The Innocent Pay the Price for the Incitement by the Preachers of Hatred, MEMRI, December 9, 2007 http://www.memritv.org/clip_transcript/en/1656.htm,
Political friendships

Source: Inner Experience

Book 1, Chapter 7 “A Well-Known Traveler” (p. 413)
The Runestaff (1969)

Source: Political Testament (1949), p. 80
Context: A real reconciliation of East and West is impossible and inconceivable on the basis of a materialistic Communism, or of a materialistic Capitalism, or indeed of a materialistic Socialism. The third way will neither be "anti-Communist" nor "anti-Capitalist". It will recognize the truth in liberal democracy, and it will equally recognize the truth in Communism. A critique of Communism and Marxism does not entail an enmity towards Soviet Russia, just as a critique of liberal democracy is not entail enmity towards the west. … But the final and most important justification of a "third way" is that there must be a place from which we may boldly testify to, and proclaim, truth, love and justice. No one today likes truth: utility and self interest have long ago been substituted for truth.

Source: The Journal of John Woolman (1774), p. 24

Source: Pieces of White Shell

Sallust, Bellum Catilinae, X, 5. This particular translation of the original Latin is from the essay "On Liberty" by Abraham Cowley: "Sallust, therefore, who was well acquainted with them both and with many such-like gentlemen of his time, says, 'That it is the nature of ambition' (Ambitio multos mortales falsos fieri coegit, etc.) 'to make men liars and cheaters; to hide the truth in their breasts, and show, like jugglers, another thing in their mouths; to cut all friendships and enmities to the measure of their own interest, and to make a good countenance without the help of good will.'" http://ibiblio.org/pub/docs/books/gutenberg/etext02/cowes10.txt The Wikiquote page for Sallust has the quote and a different translation.
Misattributed