Letter from REH to Emil Pataja, September 6, 1935.
The letter is part of ongoing correspondence with Petaja and opens with comments about a Petaja poem. “Witch’s Berceuse” appeared in the Summer 1935 issue of the amateur publication Marvel Tales of Science and Fantasy, alongside works by Ralph Milne Farley (Roger Sherman Hoar) and P. Schuyler Miller. It would be another couple of years before Petaja’s first professional published work appeared in Weird Tales.
The letter, incidentally, was included in The Collected Letters of Robert E. Howard: Volume Three: 1933-1936.
It was on sale on eBay around March 2012 for $4,999.95.
Information is at Yellowed Perils.