Shiva Purana
यावज्जीवं जपेन्नित्यमष्टोत्तरसहस्रकम् ॥ अनन्यस्तत्परो भूत्वा स याति परमां गतिम् ॥ १७ ॥
One should chant the mantra 18,000 times daily for the rest of his life. Becoming unalloyed and devoted to Him, he attains the supreme destination.
english translation
yAvajjIvaM japennityamaSTottarasahasrakam ॥ ananyastatparo bhUtvA sa yAti paramAM gatim ॥ 17 ॥
hk transliteration by Sanscript