From the Major Smoldering Stone quest introduced in the Shadows of the Past event.
You give Agent of the Arcanum Major Smoldering Stone.
Agent of the Arcanum tells you, "These crystals have many alchemical uses. Ciandra has continued to research what allows these stones to tap into this worlds well of powerful magics."
Agent of the Arcanum tells you, "Here, take this as a reward."
Agent of the Arcanum gives you Writ of Refuge.