Śrīmad-Bhāgavatam · Text 10.3.25
Who is speaking and story frame
नष्टे लोके द्विपरार्धावसाने
महाभूतेष्वादिभूतं गतेषु ।
व्यक्तेऽव्यक्तं कालवेगेन याते
भवानेक: शिष्यतेऽशेषसंज्ञ: ॥ २५ ॥
naṣṭe loke dvi-parārdhāvasāne
mahā-bhūteṣv ādi-bhūtaṁ gateṣu
vyakte ’vyaktaṁ kāla-vegena yāte
bhavān ekaḥ śiṣyate ’śeṣa-saṁjñaḥ
After millions of years, at the time of cosmic annihilation, when everything, manifested and unmanifested, is annihilated by the force of time, the five gross elements enter into the subtle conception, and the manifested categories enter into the unmanifested substance. At that time, You alone remain, and You are known as Ananta Śeṣa-nāga.
Read Śrīla Prabhupāda's purport on Vedabase.io