SRD:Fate of One

Your limited omniscience allows you to reroll a saving throw, attack roll, or skill check. Whatever the result of the reroll, you must use it even if it is worse than the original roll.

You can manifest this power instantly, quickly enough to gain its benefits in an emergency. Manifesting this power is an immediate action, like manifesting a quickened power, and it counts toward the normal limit of one quickened power per round. If you use the power to reroll a saving throw, you can manifest this power even when it is not your turn.