Kautilya's Arthashastra 7.18.36

7.18.36

arisādhāraṇaṃ yad vā tiṣṭhet tad aritaḥ śaṭham /
bhedayed bhinnam ucchindyāt tataḥ śatrum anantaram //

When a friend is as accessible to the conqueror as to the latter's enemy, the conqueror should first separate that obstinate friend from the enemy, and then destroy him, and afterwards the enemy also.