Bhagwad Gita
Chapter 8, Verse 18
अव्यक्ताद्व्यक्तयः सर्वाः प्रभवन्त्यहरागमे।
रात्र्यागमे प्रलीयन्ते तत्रैवाव्यक्तसंज्ञके।।8.18।।
When Brahma's day is manifest, this multitude of living entities comes into being, and at the arrival of Brahma's night they are all annihilated.