Arthashastra
मित्रेण आश्रितश् चेत् शत्रुर् अग्राह्ये स्थातुम् इच्छेत् सामन्त आदिभिर् मूलम् अस्य हारयेत् ॥
If the enemy, helped by his friend, shuts himself in an impregnable fort, then his neighbouring enemies may be employed to lay waste his territory.
english translation
mitreNa Azritaz cet zatrur agrAhye sthAtum icchet sAmanta Adibhir mUlam asya hArayet ॥
hk transliteration by Sanscript