Shiva Purana
पंचाक्षरमयीं विद्यां जजाप प्रणवान्विताम् ॥ नान्यत्कार्यं स वै कर्तुं लब्धवानन्तरं तदा ॥ ४५ ॥
He repeated the japas of the five-syllabled mantra with the Praṇava prefixed. He did not get any leisure to do any thing else.
english translation
paMcAkSaramayIM vidyAM jajApa praNavAnvitAm ॥ nAnyatkAryaM sa vai kartuM labdhavAnantaraM tadA ॥ 45 ॥
hk transliteration by Sanscript