Assassin's Daggers

Assassin's Daggers is a dagger. They have a 10% of inflicting Poison when wielded by Noctis or Ignis.

Source
Assassin's Daggers can be purchased from Culless Munitions in Lestallum, the Verinas Mart in Ravatogh, and the Imperial vendor outside Steyliff Grove during Chapter 7 for 1,500 gil. They can be sold back to shops for 750 gil.