Retribution Aura is an instant cast aura that surrounds the paladin. If an enemy hits the paladin or a party member within 40 yards of the paladin, the attacker will take Holy damage. Imagine a group version of Thorns (These 2 effects will stack!). The aura gains an additional 1 damage per 30.3 of the paladin's spell power.

fuente
Retribution Aura - WoWWiki - Your guide to the World of Warcraft

PD: pasa que x mas de que aumente el daño de la ret aura, el daño siempre va a ser una chota
ponele, retribution aura con un spell power promedio de 1800 hace un daño total de 171,40 sin talents
con talent (solo sactified retribution, aura mastery no se si estara andando bien) y el mismo sp pegaria 257,102