That may indeed be an original source to be preferred to the Lincoln one, which ODQ attributes as

Judgement on a book. G.W.E. Russell, Collections and Recollections ch30.

But whether Lincoln quoted Artemus Ward's supposed referee or vice versa (Lincoln & Ward overlapped as contemporaries), or whether both drew on yet another, unidentified, earlier source, my point was that the formulation far antedated both Muriel Spark and W F Buckley jnr.

≈M≈