Kautilya's Arthashastra 7.2.12

7.2.12

āsanno vāsya cchidreṣu praharet //

A powerless king should behave as a conquered king (towards his immediate enemy); but when he finds that the time of his own ascendancy is at hand due to a fatal disease, internal troubles, increase of enemies, or a friend's calamities that are vexing his enemy, then under the pretence of performing some expiatory rites to avert the danger of his enemy, he may get out (of the enemy's court); or if he is in his own territory, he should not go to see his suffering enemy; or if he is near to his enemy, he may murder the enemy when opportunity affords itself.