Thirukkural

மறைந்தவை கேட்கவற் றாகி அறிந்தவை ஐயப்பாடு இல்லதே ஒற்று.

Maraindhavai Ketkavar Raaki Arindhavai Aiyappaatu Illadhe Otru

A spy is one who is able to discover what is hidden and who retains no doubt concerning what he has known