From Pathfinder Core Rulebook, which isn't enabled.

Victorious Vigor

FEAT 5

Activity reaction

Trigger You bring a foe to 0 Hit Points

Your victories in battle fill you with pride and imbue you with the energy to fight a bit longer despite your wounds. You gain temporary Hit Points equal to your Constitution modifier until the end of your next turn.

Pathfinder Core RulebookOGL