“Look for the woman!”

Prayer and the Art of Volkswagen Maintenance (2000, Harvest House Publishers)

Il y a une femme dans toutes les affaires; aussitôt qu'on me fait un rapport, je dis: «Cherchez la femme!»
[Dumas, Alexandre, Alexandre Dumas, père, Théâtre complet, http://www.archive.org/details/thtrecomplet24dumauoft, 2009-08-07, XXIV, 1889, Michel Lévy frères, éditeurs, Paris, French, 103], translation from The Penguin Dictionary of Quotations II.iii
See wikipedia cherchez la femme on how this phrase has come to be used.
Compare Juvenal satire VI.243 (circa 100 AD), "never yet was there a lawsuit which did not have a woman at the bottom of it" (translation by G. G. Ramsay), but in that case describing the litigiousness of Roman women.
Les Mohicans de Paris (The Mohicans of Paris) (1864 play)

I've Been Waiting for You
Song lyrics, Neil Young (1968)

Source: Waiting for God

The Unknown Quantity, reported in Bartlett's Familiar Quotations, 10th ed. (1919).

Cited in " Cathy Newman: 'The internet is being written by men with an agenda' https://www.theguardian.com/media/2018/mar/19/cathy-newman-the-internet-is-being-written-by-men-with-an-agenda", 25 March 2018.

Vita Nova

As quoted in "L. M. Boyd" http://www.mediafire.com/view/ulp201hdoc2hs32/Screen%20Shot%202017-12-10%20at%203.10.58%20PM.png by Boyd, in The Sioux City Journal (April 20, 1981), p. A17