Arthashastra
प्रतिपन्नं यथा उक्तम् अभ्याघात संकुलं दर्शयित्वा रात्रौ दुर्गान् निष्क्रान्तं घातयेत् ॥
Having shown that the acknowledged ॥ enemy॥ was fraught with attacks, one should kill him at night when he has emerged from the fortress.
english translation
pratipannaM yathA uktam abhyAghAta saMkulaM darzayitvA rAtrau durgAn niSkrAntaM ghAtayet ॥
hk transliteration by Sanscript