Chapter 8 Shlokas 17, 18, 19

सहस्रयुगपर्यन्तमहर्यद्ब्रह्मणो विदु:।

रात्रिं युगसहस्रान्तां तेऽहोरात्रविदो जना:।।१७।।

अव्यक्ताद्व्यक्तय: सर्वा: प्रभवन्त्यहरागमे।

रात्र्यागमे प्रलीयन्ते तत्रैवाव्यक्तसंज्ञके।।१८।।

भूतग्राम: स एवायं भूत्वा भूत्वा प्रलीयते।

रात्र्यागमेऽवश: पार्थ प्रभवत्यहरागमे।।१९।।

Brahm’s day is equivalent to a thousand yugas; Brahm’s night is equivalent to a thousand yugas. He who realises this secret, knows the essence of both day and night.

 At the onset of day, all beings emerge from the unmanifest. With the advent of night, they merge back into that unmanifest.

Thus this entire aggregate of beings emerges again and again and, bound by its nature, is absorbed at the coming of night, only to re-emerge when day dawns.