From Pathfinder Impossible Magic, which isn't enabled.

Spell Retaliation

FEAT 6

Activity free action

Requirements Your Spellstrike isn't charged.

Trigger You succeed at a saving throw against an enemy's spell, or an enemy fails a spell attack roll against you.

Battling other spellcasters is one of your major focuses, and harnessing magic from spells you defend against gives you everything you need to fight back. You recharge your Spellstrike.

Pathfinder Impossible MagicORC