Chapter 8 · The Imperishable Absolute · Krishna said
Bhagavad Gita 8.18 — Creation and dissolution
अव्यक्ताद् व्यक्तयः सर्वाः प्रभवन्त्यहरागमे। रात्र्यागमे प्रलीयन्ते तत्रैवाव्यक्तसंज्ञके ॥
avyaktād vyaktayaḥ sarvāḥ prabhavantyaharāgame | rātryāgame pralīyante tatraivāvyaktasaṃjñake ||
Meaning
When Brahma's day dawns, all manifest things come forth from the unmanifest; when his night falls, they dissolve back into that unmanifest.