Shiva Purana
पुनश्च पंचलक्षेण मंत्रब्राह्मण उच्यते । शूद्र श्चैव नमॐतेन पंचविंशतिलक्षतः १२७ ।
He then becomes a mantrabrahmin by repeating the mantra five hundred thousand times. A Śūdra, repeating the mantra with Namaḥ at the end, for two million five hundred thousand times becomes a mantrabrahmin and so pure enough for liberation.
english translation
punazca paMcalakSeNa maMtrabrAhmaNa ucyate । zUdra zcaiva namaOMtena paMcaviMzatilakSataH 127 ।
hk transliteration by Sanscript