Variations on the “murder your darlings” saying, including “kill your darlings” and “kill your babies,” have been handed down in writing workshops and guides for decades, and almost every major 20^th century English author has been cited at one time or another. In addition to the common attribution to Faulkner—“In writing, you must kill all your darlings”—which seems to have been popularized in guides to screenwriting in the 1990s, the advice has also been attributed to Oscar Wilde, Eudora Welty, G.K. Chesterton, “the great master Chekov,” and Stephen King, who wrote, “kill your darlings, kill your darlings, even when it breaks your egocentric little scribbler’s heart, kill your darlings.”

But the earliest known example of the phrase is not from any of these writers, but rather Arthur Quiller-Couch, who spread it in his widely reprinted 1913-1914 Cambridge lectures “On the Art of Writing.” In his 1914 lecture “On Style,” he said, while railing against “extraneous Ornament”:
“If you here require a practical rule of me, I will present you with this: ‘Whenever you feel an impulse to perpetrate a piece of exceptionally fine writing, obey it—whole-hardheartedly—and delete it before sending your manuscript to press.”
Yep, that’s a darling.