CC Antya 1.101

It is said in the Padma Purāṇa, ataḥ śrī-kṛṣṇa-nāmādi na bhaved grāhyam indriyaiḥ. Chanting and hearing of the transcendental holy name of the Lord cannot be performed by the ordinary senses. The transcendental vibration of the Lord’s holy name is completely spiritual. Thus it must be received from spiritual sources and must be chanted after having been heard from a spiritual master. One who hears the chanting of the Hare Kṛṣṇa mantra must receive it from the spiritual master by aural reception. Śrīla Sanātana Gosvāmī has forbidden us to hear the holy name of Kṛṣṇa chanted by non-Vaiṣṇavas, such as professional actors and singers, for it will have no effect. It is like milk touched by the lips of a serpent, as stated in the Padma Purāṇa:

As far as possible, therefore, the devotees in the Kṛṣṇa consciousness movement gather to chant the holy name of Kṛṣṇa in public so that both the chanters and the listeners may benefit.