Arthashastra
यद् उक्तम् आत्म रक्षितके रक्ष्यं तत्र तीक्ष्णान् रसदांश् च प्रयुञ्जीत ॥
Against what is described as deserving protection in the chapter, "Safety of his own person," fiery spies and poisoners should be employed (in the enemy's court).
english translation
yad uktam Atma rakSitake rakSyaM tatra tIkSNAn rasadAMz ca prayuJjIta ॥
hk transliteration by Sanscript