The War Prayer by Mark Twain

From Wikipedia:

This piece was left unpublished by Mark Twain at his death, largely due to pressure from his family, who feared that the story would be considered sacrilegious. Twain's publisher and other friends also discouraged him from publishing it. According to one account, his illustrator Dan Beard asked him if he would publish it regardless, and Twain replied "No, I have told the whole truth in that, and only dead men can tell the truth in this world. It can be published after I am dead." Mindful of public reaction, he considered that he had a family to support, and did not want to be seen as a lunatic or fanatic.

HT: Adam