Shiva Purana
अतस्तदेव जानीयात्प्रणवं सर्वकारणम् ॥ निर्विकारी मुमुक्षुर्मां निर्गुणं परमेश्वरम्॥ ९॥
Hence he who aspires for salvation and is free from aberration shall understand Praṇava as the cause of all and me as the Nirguṇa Parameśvara.
english translation
atastadeva jAnIyAtpraNavaM sarvakAraNam ॥ nirvikArI mumukSurmAM nirguNaM paramezvaram॥ 9॥
hk transliteration by Sanscript