सहस्रयुगपर्यन्तमहर्यद् ब्रह्मणो विदुः |\nरात्रिं युगसहस्रान्तां तेऽहोरात्रविदो जनाः ||८-१७||
sahasrayugaparyantamaharyad brahmaṇo viduḥ .\nrātriṃ yugasahasrāntāṃ te.ahorātravido janāḥ ||8-17||
One day of Brahma (kalp) lasts a thousand cycles of the four ages (mahā yug) and his night also extends for the same span of time.  The wise who know this understand the reality about day and night.