Arthashastra
विस्मृते सुरुङ्गया रात्रौ राज आवासम् अनुप्रविश्य सुप्तम् अमित्रं हन्यात् ॥
and when he is forgotten, he may get out of his concealment through a tunnel, and, entering into the palace, slay his enemy while sleeping.
english translation
vismRte suruGgayA rAtrau rAja AvAsam anupravizya suptam amitraM hanyAt ॥
hk transliteration by Sanscript