Shiva Purana
ओंकारपूर्विकां तत्र संपुटान्तु नमो ऽंतगाम् ॥ शिवशक्तियुताञ्चैव शक्तिविद्यां च तादृशीम् ॥ ५८ ॥
He shall impart also the plicated Mantra beginning with Om and ending with Namaḥ and the Śaktividyā of a similar nature, accompanied by Śiva and Śakti.
english translation
oMkArapUrvikAM tatra saMpuTAntu namo 'MtagAm ॥ zivazaktiyutAJcaiva zaktividyAM ca tAdRzIm ॥ 58 ॥
hk transliteration by Sanscript