Kautilya's Arthashastra 10.2.17

10.2.17

dīrghakāntāram anudakaṃ yavasendhanodakahīnaṃ vā kṛcchrādhvānam abhiyogapraskannaṃ kṣutpipāsādhvaklāntaṃ paṅkatoyagambhīrāṇāṃ vā nadīdarīśailānām udyānāpayāne vyāsaktam ekāyanamārge śailaviṣame saṃkaṭe vā bahulībhūtaṃ niveśe prasthite visamnāhaṃ bhojanavyāsaktam āyatagatapariśrāntam avasuptaṃ vyādhimarakadurbhikṣapīḍitaṃ
vyādhitapattyaśvadvipam abhūmiṣṭhaṃ vā balavyasaneṣu vā svasainyaṃ rakṣet, parasainyaṃ cābhihanyāt //

He should protect his army when it has to pass a long desert without water; when it is without grass, firewood and water; when it has to traverse a difficult road; when it is harassed by an enemy's attacks; when it is suffering from hunger and thirst after a journey; when it is ascending or descending a mountainous country full of mire, water-pools, rivers and cataracts; when it finds itself crowded in a narrow and difficult path; when it is halting, starting or eating; when it is tired from a long march; when it is sleepy; when it is suffering from a disease, pestilence or famine; when a great portion of its infantry, cavalry and elephants is diseased; when it is not sufficiently strong; or when it is under troubles. He should destroy the enemy's army under such circumstances.