Skyrim Dragonborn: Attius Farm Clue

The clue for why Ash Spawn are attaking is found in an Ash Pile in the Attius Farm in Skyrim Dragonborn

Captain Veleth wants you to search the Old Attius Farm for clues as to why Ash Spawn are attacking, in the quest March of the Dead

The clue can be found in an Ash Pile

The clue is a Declararion of War note