Kautilya's Arthashastra 7.8.7

7.8.7

dūṣyāmitrābhyāṃ mūlahareṇa vā jyāyasā vigṛhītaṃ trātukāmas tathāvidham upakāraṃ kārayitukāmaḥ sambandhāvekṣī vā tadātve cāyatyāṃ ca lābhaṃ na pratigṛhṇīyāt //

When a king means to help another from the clutches of traitors or enemies or of a superior king threatening the very existence of the latter, and intends thereby to set an example of rendering similar help to himself in future, he should receive no profit either at the present or in the future.