Bring the Filled Vessel to Arch Druid Fandral Staghelm in Darnassus.
Without the blessings of Alexstrasza the Life-Binder and Nozdormu the Timeless, Teldrassil's growth has not been without flaw. Strange beasts have been reported arising from the very ground of the tree, and crazed furbolgs attack passing travelers.
I can only hope that the solution the Arch Druid is looking for will be found quickly. I will pour all the phials you brought into this vessel, for you to deliver to Darnassus.
Bring it to Fandral Staghelm, you will find him in the druid grove.