“There is no such thing as eternal friendship or eternal hostility–-only eternal interests.”

Source: Dune Messiah

Act IV, sc. i
Le Bourgeois Gentilhomme (1670)

Speech http://hansard.millbanksystems.com/commons/1848/mar/01/treaty-of-adrianople-charges-against to the House of Commons (1 March 1848).
1840s
Context: I hold with respect to alliances, that England is a Power sufficiently strong, sufficiently powerful, to steer her own course, and not to tie herself as an unnecessary appendage to the policy of any other Government. I hold that the real policy of England—apart from questions which involve her own particular interests, political or commercial—is to be the champion of justice and right; pursuing that course with moderation and prudence, not becoming the Quixote of the world, but giving the weight of her moral sanction and support wherever she thinks that justice is, and wherever she thinks that wrong has been done... I say that it is a narrow policy to suppose that this country or that is to be marked out as the eternal ally or the perpetual enemy of England. We have no eternal allies, and we have no perpetual enemies. Our interests are eternal and perpetual, and those interests it is our duty to follow.... And if I might be allowed to express in one sentence the principle which I think ought to guide an English Minister, I would adopt the expression of Canning, and say that with every British Minister the interests of England ought to be the shibboleth of his policy.

Source: Spinoza in der europäischen Geistesgeschichte

The Rovers, Act i, Sc. 1, reported in Bartlett's Familiar Quotations, 10th ed. (1919). Compare: "Let us embrace, and from this very moment vow an eternal misery together", Thomas Otway, The Orphan, Act iv., Sc. 2.; "My fair one, let us swear an eternal friendship", Jean Baptiste Molière, Le Bourgeois Gentilhomme (published c. 1871), act iv. sc. 1.

1960s, Why I Am Opposed to the War in Vietnam (1967)
Context: It is a sad fact that because of comfort, complacency, a morbid fear of communism, our proneness to adjust to injustice, the Western nations that initiated so much of the revolutionary spirit of the modern world have now become the arch anti-revolutionaries. This has driven many to feel that only Marxism has a revolutionary spirit. Therefore, communism is a judgment against our failure to make democracy real and follow through on the revolutions that we initiated. Our only hope today lies in our ability to recapture the revolutionary spirit and go out into a sometimes hostile world declaring eternal hostility to poverty, racism, and militarism. With this powerful commitment we shall boldly challenge the status quo, we shall boldly challenge unjust mores, and thereby speed up the day when "every valley shall be exalted, and every mountain and hill shall be made low, and the rough places shall be made plain, and the crooked places straight. And the glory of the Lord shall be revealed, and all flesh shall see it together."

Source: A Chance to Die: The Life and Legacy of Amy Carmichael

The Life of Pythagoras (1919)
Context: Fragment 4. This is the state of affairs about nature and harmony. The essence of things is eternal; it is a unique and divine nature, the knowledge of which does not belong to man. Still it would not not be possible that any of the things that are, and are known by us, should arrive to our knowledge, if this essence was not the internal foundation of the principles of which the world was founded, that is, of the finite and infinite elements. Now since these principles are not mutually similar, neither of similar nature, it would be impossible that the order of the world should have been formed by them, unless the harmony had intervened... the dissimilar things, which have neither a similar nature, nor an equivalent function, must be organized by the harmony, if they are to take their place in the connected totality of the world.

As quoted in The Law of Rewards : Giving What You Can't Keep to Gain What You Can't Lose (2003 by Randy C. Alcorn, p. 18
General sources