Lord Chaitanya says, param vijayatesri-Krishna-sankirtanam: “All glories to the chanting of sri-Krishna-sankirtana!” The maha-mantra — Hare Krishna, Hare Krishna, Krishna Krishna, Hare Hare Hare Rama, Hare Rama, Rama Rama, Hare Hare — is directly chanted by the Lord Himself, who gives us this mantra for deliverance.
Srimad Bhagavatam 1.18.7