Genre: Upanishad
Narada asked: How can I, roaming around the world, overcome the adverse effects of Kali Yuga? [1]
Brahma replied:
Here's what the Vedas imply as the means to cross Samsara (ocean of life) in the Kali Yuga: chant the name of Lord Nārāyaṇa.
Narada asked: What is that name?
Brahma replied: [2]
Line1: Hare \ Rāma \ Hare \ Rāma \
Line 2: Rāma \ Rāma \ Hare \ Hare \
Line 3: Hare \ Kṛṣṇa \ Hare \ Kṛṣṇa \
Line 4: Kṛṣṇa \ Kṛṣṇa \ Hare \ Hare \
These sixteen names destroy the āvaraṇa (coverings) of an individual surrounded by the sixteen kalās (impurities). When those are cleared, the Inner Divine shines; like the sun shines bright when the clouds screening it disperse.
Narada asked: Any rules to be observed?
Brahma replied:
There are no rules for this. [3]
Uttering this mantra umpteen times begins to cleanse us from within (karma). They are then released from all bondage of life.
Footnotes:
[1] Some scholars think this Upanishad is an extract from a larger Purana. In this tale, Narada is cursed by Daksha to roam around the world.
[2] The mantra is given as-is in the text, but it has been broken down here. This is how a mantra is shared without formally initiating anyone into it. This method is less effective when each word is a standalone mantra (as in this case), but it's still slightly better.
[3] After saying there are no rules, the Upanishad gives a rather high count of mantras to be chanted. Based on observation, this usually means that the more we chant, the better it is. From personal experience: chant with devotion; that's sufficient to give faster results than keeping counts.