Verse
सहस्रयुगपर्यन्तम् अहर्यद् ब्रह्मणो विदुः ।रात्रिं युगसहस्रान्तां तेऽहोरात्रविदो जनाः ॥
Those who know the day of Brahma, a thousand ages (Yugas) in duration, and the night, a thousand ages in ending, they are the knowers of day and night.
Gītā 8·17