It says it's attributed to Ernest Hemingway but that claim seems unlikely.
The claim of Hemingway's authorship originates in an unsubstantiated anecdote about a wager among him and other writers. Hemingway is said to have claimed he could write a short story only six words short. In a 1991 letter to Canadian humorist John Robert Colombo, science fiction writer Arthur C. Clarke recounts: "He's [Hemingway] supposed to have won a $10 bet (no small sum in the '20s) from his fellow writers. They paid up without a word. ... Here it is. I still can't think of it without crying— FOR SALE. BABY SHOES. NEVER WORN."[1]