Instrument of Zeal
FEAT 16 Blessed Counterstrike feat or Retributive Strike reaction, champion's reaction that grants an ally resistance to an enemy's damage (including the grandeur, justice, liberation, and redemption causes)
Divine energy fills your weapon. Whenever you critically hit an enemy with Blessed Counterstrike or Retributive Strike, your attack deals an extra weapon damage die, and the target is Slowed 1 on its next turn
Pathfinder Player Core 2ORC