Nīlakaṇṭha-nāmotpatti-kathana
Origin of the Epithet “Nīlakaṇṭha”
साध्या विद्याधरा नागाश्चारणाश्च तपोधनाः / वालखिल्या महात्मानस्तपः सिद्धाश्च सुव्रताः
sādhyā vidyādharā nāgāścāraṇāśca tapodhanāḥ / vālakhilyā mahātmānastapaḥ siddhāśca suvratāḥ
There are the Sādhyas, Vidyādharas, Nāgas, and Cāraṇas, rich in the treasure of tapas; and also the Vālakhilya great souls, the ascetic siddhas, and those of pure vows.