Arthashastra
मित्रं बन्धुं वा अपदिश्य योग पुरुषाः शासन मुद्रा हस्ताः प्रविश्य दुर्गं ग्राहयेयुः ॥
Spies, disguised as friends or relatives and with passports and orders in their hands, may enter the enemy's fort and help to its capture.
english translation
mitraM bandhuM vA apadizya yoga puruSAH zAsana mudrA hastAH pravizya durgaM grAhayeyuH ॥
hk transliteration by Sanscript