Jnana, Tilasini and others are singing the Mahamantra.
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You can get the text to the mantra here.
The Hare Krishna mantra, also referred to reverentially as the Maha Mantra ("Great Mantra"), is a 16-word Vaishnava mantra which is mentioned in the Kali-Santarana Upanishad, and which from the 15th century rose to importance in the Bhakti movement following the teachings of Chaitanya Mahaprabhu.