In The Sacred Flame (part 3), you must infiltrate the Galak Centaur's camp to the north and enter the cave there, known as Splithoof Hold. Deep in the cave, you must douse their sacred flame and steal the [Cloven Hoof].
Head north from Freewind Post and enter the centaur camp at Splithoof Crag. In the center of the camp against the northern cliffs there will be an entrance to the cave, that's Splithoof Hold. The centaur in here are stronger than those outside, so beware. At the very back of the cave you will find two lvl 30 centaur guarding a flame. You'll want to defeat them before attempting to douse it, and since it's impossible to pull just one, this can be tricky. It might be wise to get a small group for this one because of this.
Once you have access to the flame, right click it to get the [Cloven Hoof].
Using the water you brought, you will be able to temporarily douse the flame that holds the centaur relic. It will not work permanently, however, so you will have to be quick about it.
You will find Splithoof Crag, the centaurs' stronghold, to the north of here. The flame is kept in Splithoof Hold, a heavily guarded part of the crag.
Be careful, though, the Galak centaur have great numbers here, and will be rather reluctant to surrender something so dear to them.
Rewards
You will be allowed to chose one of the following: