Shiva Purana
तस्मान्मज्ज्ञानसिद्ध्यर्थं मंत्रमॐकारनामकम् । इतः परं प्रजपतं मामकं मानभंजनम् १५ ।
Hence, hereafter, both of you shall start reciting the mantra Oṃkāra to acquire knowledge of me. It shall quell your false pride as well.
english translation
tasmAnmajjJAnasiddhyarthaM maMtramaOMkAranAmakam । itaH paraM prajapataM mAmakaM mAnabhaMjanam 15 ।
hk transliteration by Sanscript