Your autoattacks have a 8% chance to grant Hand of Light, causing your next Holy Power ability to consume no Holy Power and to cast as if 3 Holy Power were consumed. Each point of Mastery increases the chance by an additional 1%.
Hand of Light is the PaladinMastery for the Retribution tree. It gives the Paladin the ability to sometimes use Holy Power-requiring spells without having Holy Power, additionally treating them as if the Paladin had a maximum amount of it.
Patch 4.0.1 (2010-10-12): Added in this patch. 
