Śrīmad-Bhāgavatam · Text 1.19.7
Who is speaking and story frame
इति व्यवच्छिद्य स पाण्डवेय:
प्रायोपवेशं प्रति विष्णुपद्याम् ।
दधौ मुकुन्दाङ्घ्रिमनन्यभावो
मुनिव्रतो मुक्तसमस्तसङ्ग: ॥ ७ ॥
iti vyavacchidya sa pāṇḍaveyaḥ
prāyopaveśaṁ prati viṣṇu-padyām
dadhau mukundāṅghrim ananya-bhāvo
muni-vrato mukta-samasta-saṅgaḥ
Thus the King, the worthy descendant of the Pāṇḍavas, decided once and for all and sat on the Ganges’ bank to fast until death and give himself up to the lotus feet of Lord Kṛṣṇa, who alone is able to award liberation. So, freeing himself from all kinds of associations and attachments, he accepted the vows of a sage.
Read Śrīla Prabhupāda's purport on Vedabase.io