The Tear of Asha is an artifact from Heroes of Might and Magic V and Might & Magic: Heroes VI. It is similar to the grail from Heroes III and Heroes IV, and can be used to construct a grail building. Every faction has its own unique grail building, with different bonuses, but usually includes a large increase to income and creature growth, and some other bonus.
In Heroes V, the Tear of Asha is found by collecting pieces of the puzzle map from visiting obelisks. The puzzle map will show its location and the player will have to dig for it. There is never more than one Tear of Asha on each map, but sometimes, there's none.
In Heroes VI, it can be found by combining the four Fragments of the Moon Disc, and following the flash that appears on the mini-map. Each skirmish map may have multiple Tears of Asha.