I have a number of Mark Twain journalistic contributions
available online in searchable format at:

http://www.twainquotes.com

A search for the keywords hash and hasheesh produced these first
hand testimonials:

~~~~~
From the _Golden Era_, Oct. 11, 1863 - "The Great Prize Fight"

"I determined to be upon the ground at an early hour. Now I dislike to be
exploded, as it were, out of my balmy slumbers, by a sudden, stormy
assault upon my door, and an imperative order to "Get up!" - wherefore I
requested one of the intelligent porters of the Lick House to call at my
palatial apartments, and murmur gently through the key-hole the magic
monosyllable "Hash!" That "fetched me."

~~~~~

From the _Alta California_, March 3, 1868 in an article titled "Mark Twain
on His Travels" wherein he critiques the play "The White Fawn":

"I think these hundreds of princely costumes are changed every fifteen
minutes during half the night; splendid pageants are filing about the
stage constantly, yet one seems never to see the same dress twice. The
final grand transformation scene is a vision of magnificence such as no
man could imagine unless he had eaten a barrel of hasheesh."

~~~~~

There are other scattered references in my online collection
as well as a few that can be found on the searchable text CD of
_Twain's World_.

Barb