Vedic Scource Of Hare Krishna Mahamantra

The Kali-Santāraṇa Upaniṣad 

Kalisaṇṭāraṇopaniṣad (कलिसण्टारणोपनिषद्) is a Vedantic text associated with the Kṛṣṇa Yajurveda. 

It is the source of the "Hare Kṛṣṇa" Mahamantra,
 explaining that 

"These sixteen words are destructive 

of the evil effects of Kali Yuga."

Hare Krishna Hare Krishna

    Krishna Krishna Hare Hare

    Hare Rama Hare Rama

    Rama Rama Hare Hare