Hourglass of Fate

From Editable Codex

The Hourglass of Fate not only enables the monks to return him/her to life after being mortally wounded, but also was used by the Avatar to call a monk, if a companion had died. The Hourglass of Fate was designed so that the monks could determine when certain events drew nigh. It was said to contain ‘the lifeblood of Serpent Isle’. If it runs out, the world will end.

Thoxa gave it to the Avatar right at the beginning of Ultima VII/2.