"The chanting of the five-syllabled mantra shall always be performed along with Om" ~ Shiva Purana.

Namah Shivaya! Potent Mantra of Shiva that Parvati recited during her penance to win Shiva. the great sage Narada asked Parvati to recite the five-syllabled mantra of Shiva, calling it the king of all mantras and informed her that its continuous chanting was the most effective way of propitiating him. "The chanting of the five-syllabled mantra shall always be performed along with Om" ~ Shiva Purana. Thus the potent mantra becomes Om Namah Shivaya! "This mantra is of the nature of Shiva himself. By holding on to the mantra, the physical body of the devotee becomes identified with Shiva" ~ Shiva Purana.
Jai ShivaShakti ~ Jai ShankarParvati!!