Love Unending

Although it is not specifically said, killing the Time-Lost mobs will drop Ephemeral Sand for the quest. I don't know if it's 100% drop, but I did get 1 drop for every mob I killed.

Do NOT go into the portal. Fly down below the platform and farm along the river bed.

This is the 2nd in the quest chain of Tarecgosa's Rest. You can only get this and the subsequent quests, if you've previously obtained Dragonwrath, Tarecgosa's Rest which is class restricted. So if you're not a Priest, Shaman, Mage, Warlock, Druid, or Evoker and meet the prereqs (other quests too but more info on comments of the first quest linked here) you will never see this and subsequent quests.