Kautilya's Arthashastra 7.9.39

7.9.39

ṛte yad arthaṃ praṇayād rakṣyate yac ca rakṣati /
pūrvopacitasambandhaṃ tan mitraṃ nityam ucyate //

that friend who maintains friendship with disinterested motives and merely for the sake of friendship and by whom the relationship acquired of old is kept intact, is a long-standing friend;