Shiva Purana
शिवया परया शक्त्या संयुक्तं परमेश्वरम् ॥ संचिंत्य हृदये प्रीत्या तेपे स परमं तपः॥६॥
Within his heart he pondered lovingly over lord Śiva united with the great Śakti called Śivā. He then performed great penance.
english translation
zivayA parayA zaktyA saMyuktaM paramezvaram ॥ saMciMtya hRdaye prItyA tepe sa paramaM tapaH॥6॥
hk transliteration by Sanscript