Shiva Purana
एतं यंत्रं समालिख्य प्रणवे नव वेष्टयेत् ॥ तदुत्थेनैव नादेन विद्यन्नादावसानकम् ॥ १८ ॥
The Yantra is encompassed by the Praṇava itself. The Nāda shall be known through the Nāda arising therefrom.
english translation
etaM yaMtraM samAlikhya praNave nava veSTayet ॥ tadutthenaiva nAdena vidyannAdAvasAnakam ॥ 18 ॥
hk transliteration by Sanscript