Yuga-Vibhāga and Kāla-Pramāṇa
Measures of Time and the Four Yugas
कलिं वर्षसरस्रं तु युगमाहुर्द्विजोत्तमाः / तस्यैकशतिका संध्या संध्यांशः संध्यया समः
kaliṃ varṣasarasraṃ tu yugamāhurdvijottamāḥ / tasyaikaśatikā saṃdhyā saṃdhyāṃśaḥ saṃdhyayā samaḥ
The foremost Brahmins declare that the Kali Yuga is a thousand years in length. Its twilight is one hundred years, and the twilight portion is equal to that twilight.