Kural - 586

As monk or devotee, through every hindrance making way,
A spy, whate'er men do, must watchful mind display

Explanation
He is a spy who, assuming the appearance of an ascetic, goes into (whatever place he wishes), examines into (all, that is needful), and never discovers himself, whatever may be done to him.

Tamil Transliteration
Thurandhaar Pativaththa Raaki Irandhaaraaindhu
Enseyinum Sorviladhu Otru.