Bhagavatapurana 3.11.19

3.11.19

catvāri trīṇi dve caikaṃ kṛtādiṣu yathā-kramam /
saṅkhyātāni sahasrāṇi dvi-guṇāni śatāni ca //

19 & 20. The yugas respectively consist of four thousands, three thousands, two thousands, and one thousand years; the transition periods at the beginning and the end also respectively consist of eight hundreds, six hundreds, four hundreds and two hundreds of years; and the wise who know the fact call that a yuga which is between the transition periods counted by hundreds and only in relation to such yugas Dharma is laid down in the Holy books.