BG 8.17
सहस्रयुगपर्यन्तमहर्यद्ब्रह्मणो विदुः। रात्रिं युगसहस्रान्तां तेऽहोरात्रविदो जनाः
sahasra-yuga-paryantam ahar yad brahmaṇo viduḥ rātriṁ yuga-sahasrāntāṁ te ’ho-rātra-vido janāḥ
Those who understand the cosmic day and night know that one day of creation is a thousand cycles, and that the night is of equal length.
Translated by Shri Purohit Swami
Those who know the day of Brahma, which lasts a thousand Yugas, and the night, which also lasts a thousand Yugas, know day and night.
Translated by Swami Sivananda
Word meanings (from the gita/gita dataset)
sahasra—one thousand; yuga—age; paryantam—until; ahaḥ—one day; yat—which; brahmaṇaḥ—of Brahma; viduḥ—know; rātrim—night; yuga-sahasra-antām—lasts one thousand yugas; te—they; ahaḥ-rātra-vidaḥ—those who know his day and night; janāḥ—people