Kautilya's Arthashastra 7.2.25

7.2.25

priyo yasya bhaved yo vā priyo 'sya kataras tayoḥ /
priyo yasya sa taṃ gacched ity āśrayagatiḥ parā //E

Of two powerful kings who are on amicable terms with each other, a king shall make alliance with one of them who likes him and whom he likes; this is the best way of making alliance.