Shiva Purana
तेनाधीतं श्रुतं तेन कृतं सर्वमनुष्ठितम् ॥ येनोन्नमश्शिवायेति मंत्राभ्यासः स्थिरीकृतः ॥ ३५ ॥
If anyone has stabilised the Mantra “Oṃ Namaḥ Śivāya” by frequent practice, he has learnt all, heard all and performed all.
english translation
tenAdhItaM zrutaM tena kRtaM sarvamanuSThitam ॥ yenonnamazzivAyeti maMtrAbhyAsaH sthirIkRtaH ॥ 35 ॥
hk transliteration by Sanscript