Shiva Purana

siva.sh/siva-purana/kotirudra-samhita/30/32

ज्योतिर्लिंगस्वरूपो हि नाम्ना नागेश्वरश्शिवः ।। नागेश्वरी शिवा देवी बभूव च सतां प्रियौ ।। ३२ ।।

sanskrit

The Jyotirliṅga form of Śiva came to be known as Nāgeśvara. Goddess Śivā became Nāgeśvarī. Both of them are favourites of the devotees.

english translation

jyotirliMgasvarUpo hi nAmnA nAgezvarazzivaH || nAgezvarI zivA devI babhUva ca satAM priyau || 32 ||

hk transliteration by Sanscript