“I often find poems hand written in old abandoned notebooks.”

Interview in The Review, published by Ian Hamilton (1972)

Source: City of Lost Souls

Qu'on me donne six lignes écrites de la main du plus honnête homme, j'y trouverai de quoi le faire pendre.
As quoted in The Cyclopedia of Practical Quotations (1896) by Jehiel K̀eeler Hoyt, p. 763
Édouard Fournier, in L'Espirit dans l'Historie (1867), 3rd edition, Ch. 51, p. 260, disputes the traditional attribution, and suggests various agents of Richelieu might have been the actual author.
David Hackett Fischer, in Champlain's Dream (2009), Simon & Schuster, p. 704, n. 14, says it's a paraphrase of Quintilian and there is no source closer to Richelieu than Francoise Bertaut's Memoires pour servir à l'histoire d'Anne d'Autriche.
Disputed

The Poetic Principle (1850)

"How Awful When Poetry Ages As It Is Read"
I've Learned Some Things (2008)
Context: Gulls into the water, women proudly into the bazaars
I was going to write a poem, I was stifling, fed up with old things
Eat, my mother says, but they're all things I've grown accustomed to, in the end.
Like Camus and — I don’t know — people like that, I'm cracking up
Everything will begin when it untangles itself from your hair

As quoted in The Quotable Woman (1978) by Elaine T Partnow, p. 226. "When men destroy their old gods they will find new ones to take their place" has sometimes been quoted as her original statement, though she states that she herself is quoting an abbot.

The Paris Review, "Writers at Work: 4th series," interview with Peter Buckman and William Fifield (1969).
General sources