The Australian Association of Writing Programs

Sources of earlier Hemingway quotes: the one that begins "If a writer of prose knows enough about what he is writing about..." comes from Death in the Afternoon, p. 192. {All quotes refer to Scribner paperback editions of H's work.]

The second quote about 'write about it don't talk about it' I couldn't find. I read the whole book [Phlllips, Larry W. Ernest Hemingway on Writing] twice (it's only a little book) but may have missed it in a larger quote.

It is a fascinating book full of great quotes. One of my newly discovered favourites is "My attitude toward punctuation is that it ought to be as conventional as possible. The game of golf would lose a good deal if croquet mallets and billiard cues were allowed on the putting green. You ought to be able to show that you can do it a good deal beter than anyone else with the regular tools before you have a license to bring in your own improvements." [from a letter to Horace Liverright, 1925 from Selected Letters, p. 161. 

regards, BME