Shiva Purana
उभयोर्वादशमने यद्रूपं स दर्शितं बुधाः ॥ महादेवेति विख्यातं निर्गुणेन शिवेन हि ॥ ७ ॥
The form that was revealed by Nirguṇa Śiva at the time of subduing the dispute between the two is, O learned ones, famous as Mahādeva.
english translation
ubhayorvAdazamane yadrUpaM sa darzitaM budhAH ॥ mahAdeveti vikhyAtaM nirguNena zivena hi ॥ 7 ॥
hk transliteration by Sanscript