Kautilya's Arthashastra 7.7.8

7.7.8

paṇitas tasyāpakārasamartho vikrameta, anyathā saṃdadhyāt //

When a king of superior power is involved in troubles, or is come to grief or is afflicted with misfortune, his enemy, though of inferior power, may request of him the help of his army in return for a share in the profit proportional to the strength of the army supplied. If the king to whom peace is offered on such terms is powerful enough to retaliate, he may declare war; and otherwise he may accept the terms.