Valmiki Ramayana Kishkindha Kanda Sarga 2 Shloka 22
Original Shlokaअरयश्च मनुष्येण विज्ञेयाश्छद्मचारिणः। विश्वस्तानामविश्वस्तारन्ध्रेषु प्रहरन्ति हि4.2.22।।
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मनुष्येण by a man, छद्मचारिणः spies who move about in disguise, अरयः enemies, विज्ञेयाः they should be identified, अविश्वस्ताः who do not trust, विश्वस्तानाम् of the trusting men, रन्ध्रेषु when we are not vigilant प्रहरन्ति, हि will strike
'One has to identify these men roaming in disguise. These are not trustworthy and could even be our enemies, making us believe them so as to attack us when we are not vigilant.