This quest is not available in game.
Use the Extinguishing Mixture near the eternal flame in the Alonsus Chapel to remove the Light's protection. Be prepared to fight anyone who may attempt to defend the chapel.
Ours is the true way of utilizing the Light, <name>. To show others that would call themselves 'paladins' the folly of their ways, I intend to send an unmistakable message.
The Alonsus Chapel, where the Order of the Silver Hand was founded, seems immune to the destruction of Stratholme. The chapel's eternal flame affords it the Light's protection, but when you use this mixture to extinguish the flame, that protection will be no more. It will burn, and our dominion over the Light will be proven to the world.