If a limb of one's body is poisoned by disease, it must be amputated so that the rest of the body may live happily. Similarly, even one's own son, if unfavorable, must be rejected, although born of one's own body
SB Canto 7
Although a medicinal herb, being born in the forest, does not belong to the same category as a man, if beneficial it is kept very carefully. Similarly, if someone outside one's family is favorable, he should be given protection like a son. On the other hand, if a limb of one's body is poisoned by disease, it must be amputated so that the rest of the body may live happily. Similarly, even one's own son, if unfavorable, must be rejected, although born of one's own body.
Śrī Caitanya Mahāprabhu has instructed all devotees of the Lord to be humbler than the grass and more tolerant than trees; otherwise there will always be disturbances to their execution of devotional service. Here is a vivid example of how a devotee is disturbed by a nondevotee, even though the nondevotee is an affectionate father. The material world is such that a nondevotee father becomes an enemy of a devotee son. Having determined to kill even his son, Hiraṇyakaśipu gave the example of amputating a part of one's body that has become septic and therefore injurious to the rest of the body. The same example, of course, may also be applied to nondevotees. Cāṇakya Paṇḍita advises, tyaja durjana-saṁsargaṁ bhaja sādhu-samāgamam. Devotees actually serious about advancing in spiritual life should give up the company of nondevotees and always keep company with devotees. To be too attached to material existence is ignorance because material existence is temporary and miserable. Therefore devotees who are determined to perform tapasya (penances and austerities) to realize the self, and who are determined to become advanced in spiritual consciousness, must give up the company of atheistic nondevotees. Prahlāda Mahārāja maintained an attitude of noncooperation with the philosophy of his father, Hiraṇyakaśipu, yet he was tolerant and humble. Hiraṇyakaśipu, however, being a nondevotee, was so polluted that he was even prepared to kill his own son. He justified this by putting forward the logic of amputation.