The passage is from _Following the Equator_, also titled _More
Tramps Abroad_. In the Oxford edition reprint of _Following
the Equator_, it is on p. 688.

Taking portions of Twain's works out of context and reprinting
them as "new" material, interviews or stories seems to have
been common practice. This is becoming very evident as more
and more historical newspaper archives are becoming text
searchable. It also requires researchers and collectors to
do more study to determine sources of what -- at first glance --
seems like new material.