Vishnupurana 2.16.17

2.16.17

ṛbhur uvāca:
tavopadeśadānāya pūrvaśuśrūṣaṇādṛtaḥ
gurus te 'ham ṛbhur nāmnā nidāgha samupāgataḥ //

"When Nidágha heard these words, he immediately fell at the feet o the stranger, and said, Of a surety thou art my saintly preceptor Ribhu the mind of no other person is so fully imbued with the doctrines of unity as that of my teacher, and hence I know that thou art he.' To this Ribhu replied, 'I am your preceptor, by name Ribhu, who, pleased with: the dutiful attention he has received, has come to Nidágha to give him instruction: for this purpose have I briefly intimated to you divine truth, the essence of which is the non-duality of all.' Having thus spoken to Nidágha, the Brahman Ribhu went away, leaving his disciple profoundly impressed, by his instructions, with belief in unity. He beheld all beings thenceforth as the same with himself, and, perfect in holy knowledge, obtained final liberation.