Mahabharata 3.149.40

3.149.40

tasmāddeśe ca durge ca śatrumitrabaleṣu ca |
nityaṃ cāreṇa boddhavyaṃ sthānaṃ vṛddhiḥ kṣayastathā || 40 ||

Therefore, it is necessary to ascertain through spies the nature of the hostile country, its fortified places and the allied force of the enemy and their prosperity and decay and the way in which they retain the adhesion of the powers they have drawn to their side. Spies are among the important auxiliaries of the king; and tact, diplomacy, prowess, chastisement, favour and cleverness lead to success. And success is to be attained through these, either in separation, or combined--namely, conciliation, gift, sowing dissensions, chastisement, and sight. And, O chief of the Bharatas, polity hath for its root diplomacy; and diplomacy also is the main qualification of spies. And polity, if well judged conferreth success. Therefore, in matters of polity the counsels of Brahmanas should be resorted to. And in secret affairs, these should not be consulted,--namely, a woman, a sot, a boy, a covetous person a mean-minded individual, and he that betrayeth signs of insanity. Wise men only should be consulted, and affairs are to be despatched through officers that are able.