Shiva Purana
आधारशक्तिमारभ्य शुद्धविद्यासनावधि ॥ ॐकारादिचतुर्थ्यंतं नाममन्त्रं नमोन्तकम् ॥ ३८ ॥
From the base power to the pure knowledge seat. The fourth syllable of the name mantra, beginning with the omkara, is the end of the name.
english translation
AdhArazaktimArabhya zuddhavidyAsanAvadhi ॥ OMkArAdicaturthyaMtaM nAmamantraM namontakam ॥ 38 ॥
hk transliteration by Sanscript