SB 6.16.5

bandhu-jñāty-ari-madhyastha-
 mitrodāsīna-vidviṣaḥ
sarva eva hi sarveṣāṁ
 bhavanti kramaśo mithaḥ
Word for word: 
bandhu — friends; jñāti — family members; ari — enemies; madhyastha — neutrals; mitra — well-wishers; udāsīna — indifferent; vidviṣaḥ — or envious persons; sarve — all; eva — indeed; hi — certainly; sarveṣām — of all; bhavanti — become; kramaśaḥ — gradually; mithaḥ — of one another.
Translation: 
In this material world, which advances like a river that carries away the living entity, all people become friends, relatives and enemies in due course of time. They also act neutrally, they mediate, they despise one another, and they act in many other relationships. Nonetheless, despite these various transactions, no one is permanently related.
Purport: 

It is our practical experience in this material world that the same person who is one’s friend today becomes one’s enemy tomorrow. Our relationships as friends or enemies, family men or outsiders, are actually the results of our different dealings. Citraketu Mahārāja was lamenting for his son, who was now dead, but he could have considered the situation otherwise. “This living entity,” he could have thought, “was my enemy in my last life, and now, having appeared as my son, he is prematurely leaving just to give me pain and agony.” Why should he not consider his dead son his former enemy and instead of lamenting be jubilant because of an enemy’s death? As stated in Bhagavad-gītā (3.27), prakṛteḥ kriyamāṇāni guṇaiḥ karmāṇi sarvaśaḥ: factually everything is happening because of our association with the modes of material nature. Therefore one who is my friend today in association with the mode of goodness may be my enemy tomorrow in association with the modes of passion and ignorance. As the modes of material nature work, in illusion we accept others as friends, enemies, sons or fathers in terms of the reactions of different dealings under different conditions.