I had this message form a PhD student. Can anyone help....

I'm working on a novel (Percival Everett's "Erasure") that attributes its
epigraph to Twain's "Following the Equator": "I could never tell a lie that
anybody would doubt nor a truth that anybody would believe."

I've done exhaustive searches of hypertexts of "the Equator" and can't find
this anywhere! I'm wondering if Everett has made it up, which would fit well
with the novel because it's concerned with issues of authorship/literary
hoaxes etc.  Or am I just missing it?