Manusmriti

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चत्वार्याहुः सहस्राणि वर्षाणां तत् कृतं युगम् । तस्य तावत्शती सन्ध्या सन्ध्यांशश्च तथाविधः ॥ ६९ ॥

sanskrit

They declare that the Krita age (consists of) four thousand years (of the gods); the twilight preceding it consists of as many hundreds, and the twilight following it of the same number.

english translation

catvAryAhuH sahasrANi varSANAM tat kRtaM yugam | tasya tAvatzatI sandhyA sandhyAMzazca tathAvidhaH || 69 ||

hk transliteration by Sanscript