Mahabharata 12.69.18

12.69.18

yo nopakartuṃ śaknoti nāpakartuṃ mahīpatiḥ |
aśakyarūpaścoddhartumupekṣyastādṛśo bhavet || 18 ||

He should also, O bull of Bharata's race, know the spies of his foes by himself setting spies in shops and places of amusement, and concourses of people, among beggars, in his pleasure gardens and parks, in meetings and conclaves of the learned, in the country, in public places, in places where he holds his own court, and in the houses of the citizens. The king possessed of intelligence may thus ascertain the spies despatched by his foes. If these be known, the king may derive much benefit, O son of Pandu! When the king, by a survey of his own, finds himself weak, he should then, consulting with his counsellors make peace with a foe that is stronger. The king that is wise should speedily make peace with a foe, even when he knows that he is not weak, if any advantage is to be derived from it. Engaged in protecting his kingdom with righteousness, the king should make peace with those that are possessed of every accomplishment, capable of great exertion, virtuous, and honest. When the king finds himself threatened with danger and about to be overtaken by ruin, he should slay all offenders whom he had overlooked before and all such persons as are pointed at by the people. A king should have nothing to do with that person who can neither benefit nor injure him, or with one who cannot rescue himself from distress.