SB 6.16.5
bandhu-jñaty-ari-madhyastha-
mitrodasina-vidvisah
sarva eva hi sarvesam
bhavanti kramaso mithah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
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 by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
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 Maharaja 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-gita (3.27), prakrteh kriyamanani gunaih karmani sarvasah: 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.