A Prisoner's Journal is a Diablo III record, found on level 2 of the Halls of Agony in Act I of Diablo III. It will drop after completing the event "A Stranger in Need". Collecting it will add to the A Quick Study achievement.
It reads as follows:
13th day of Lunasadh, 1263, Anno Kehjistani, The jailers burned runes into my flesh. They say all the torture and dark magic will turn us into demonic slaves for King Leoric. What foolish lies! 17th day of Lunasadh, Pain is terrible...I can't think...I'm so hungrrry. 20th day of Lunasadh, MMMmmMMMASTter I HunnGEr MASTER FeEEED ME.