Prabhupāda: There is a version by Rāmānujācārya. Rāmānujācārya, he was a great ācārya of this Vaiṣṇava sampradāya. His spiritual master gave him mantra: "My dear boy, you chant this mantra silently. Nobody can hear. It is very..." So then he asked, "What is the effect of this mantra?" He said, "By chanting this mantra, by meditation, you'll get liberation." So he immediately went out and in a public, big meeting he said that "You chant this mantra. You'll be all liberated." (laughter) .
So he came back to his spiritual master, and his spiritual master was very angry that "I told you that you should chant silently." He said, "Yes, I have committed offense. So whatever punishment you like, you can give me. But because you told me that this mantra will liberate, I have given it publicly. Let everyone hear and be liberated. Let me go to hell. I don't mind. I have disobeyed your order. Let me go to hell. I am prepared. But by this chanting mantra, if anyone is liberated, let it be publicly distributed." His spiritual master embraced him: "You are greater than me." You see? So if a mantra has so power, why it should be secret? It should be distributed. People are suffering. So Caitanya Mahāprabhu said, "Chant this Hare Kṛṣṇa mantra. Anyone who will hear... Even the birds and beasts will hear and they will be liberated." That's all.
Room Conversation With John Lennon, Yoko Ono, and George Harrison -- September 11, 1969, London, At Tittenhurst