Shiva Purana
ज्योतिर्लिंगस्वरूपो हि नाम्ना नागेश्वरश्शिवः ॥ नागेश्वरी शिवा देवी बभूव च सतां प्रियौ ॥ ३२ ॥
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