Encrypted Twilight Text

Source
The Encrypted Twilight Text drops only from the following members of the Twilight's Hammer.
 * Twilight Prophet
 * Twilight Marauder Morna
 * Twilight Overlord
 * Twilight Master
 * Twilight Flamereaver
 * Twilight Avenger
 * Twilight Geolord
 * Twilight Stonecaller
 * Twilight Lord Everun
 * Twilight Marauder

As a quest objective
The Encrypted Twilight Text is an objective of the following quests:
 * Secret Communication
 * Encrypted Twilight Texts
 * True Believers
 * Still Believing