Desiring to bestow His mercy upon the saintly Mārkaṇḍeya, who had perfectly fixed his mind in self-realization through penance, Vedic study and observance of regulative principles, the Supreme Personality of Godhead personally appeared before the sage in the forms of Nara and Nārāyaṇa.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
तस्यैवं युञ्जतश्चित्तं तपःस्वाध्यायसंयमैः । अनुग्रहायाविरासीन्नरनारायणो हरिः
tasyaivaṃ yuñjataścittaṃ tapaḥsvādhyāyasaṃyamaiḥ | anugrahāyāvirāsīnnaranārāyaṇo hariḥ
SB 12.8.32