Om Namah Shivaya
Om Namaḥ Śivāya is one of the most popular Hindu Mantras.
Namah Shivaya means "O salutations to the auspicious one!", or “adoration to Lord Shiva". It is called Shiva Panchakshara,meaning the "five-syllable" mantra (viz., excluding the Om) and is dedicated to Lord Shiva and his universal oneness of five elements:
Na sound represents earth
Ma sound represents water
Śi sound represents fire
Vā sound represents Pranic air
Ya sound represents sky or ether
Its total meaning is that "universal consciousness is one".
Traditionally the five letters also represent:
Na - the Lord’s concealing grace
Ma - the world
Śi - standing for Shiva
Vā - His revealing grace
Ya - the Ātman or soul
The Tirumantiram (a Vedic scripture) announces, “His feet are the letter Na. His navel is the letter Ma. His shoulders are the letter Śi. His mouth, the letter Vā. His radiant cranial centre aloft is Ya. Thus is the five-lettered form of Shiva.”: Tirumantiram 941.
This mantra is repeated verbally or mentally, drawing the mind in upon itself to Lord Shiva’s infinite, all-pervasive presence. Traditionally it is repeated 108, or 1008 times a day while keeping count on a strand of rudraksha beads. It is freely sung and chanted by everyone, but it is most powerful when given by one’s guru. This mantra is associated with qualities of prayer, divine-love, grace, truth, and blissfulness. When done correctly, it calms the mind and brings spiritual insight and knowledge. It also keeps the devotee close to Shiva and within His protective global fellowship.
Traditionally, it is accepted to be a powerful healing mantra beneficial for all physical and mental ailments. Soulful recitation of this mantra brings peace to the heart and joy to the Ātman or soul. Many Hindu teachers consider that the recitation of these syllables is sound therapy for the body and nectar for the Ātman. The nature of the mantra is the calling upon the higher self; it is the calling upon Shiva.
source Wikipedia
There are many recordings of the chanting of this Mantra. Here is a very devotional one called One Heart:
Print