Kautilya's Arthashastra 2.35.13

2.35.13

evaṃ samāhartṛpradiṣṭās tāpasavyañjanāḥ karṣakagorakṣakavaidehakānām adhyakṣāṇāṃ ca śaucāśaucaṃ vidyuḥ //

Similarly spies under the guise of ascetics shall, as ordered by the Collector-general, gather information as to the proceedings, honest or dishonest, of cultivators, cow-herds, merchants, and heads of Government departments.