Shiva Purana
तस्मात्तपांसि यज्ञाश्च व्रतानि नियमास्तथा ॥ पञ्चाक्षरार्चनस्यैते कोट्यंशेनापि नो समः ॥ १३ ॥
Hence, penances, sacrifices, observances and holy rites are not equal to even a croreth part of the worship with the five-syllabled mantra.
english translation
tasmAttapAMsi yajJAzca vratAni niyamAstathA ॥ paJcAkSarArcanasyaite koTyaMzenApi no samaH ॥ 13 ॥
hk transliteration by Sanscript