Manava Dharmashastra 1.73

1.73

yugasahasramanto yasyāhastadvaiyugasahasrāntam | ye mānuṣyā etajjānate te'horātraviduḥ | kiṃ teṣāmityapekṣāyāṃ puṇyaṃ bhavatīti sambandhaḥ | brāhmasyāhnaḥ parimāyavedanaṃ puṇyamatastadveditavyamiti stutyā vidhipratipattiḥ |

Those who know the ‘Day of Brahmā’ as ending with the (said) thousand ‘time-cycles,’ and the ‘night’ also as of the same extent,—are people who alone know what is ‘day and night’, and acquire merit.—(73)

Medhātithi’s commentary (manubhāṣya):
‘Yugasahasrāntam,’—‘that of which the thousand cycles are the end;’—those men who know this, ‘they are the people who alone know what is Day and Night.’

If it be asked—what happens to the people who know this?—it is added that ‘they acquire merit.’ Such is the connection (of the word ‘puṇyam’). The sense is that ‘knowledge of Brahmā’s Day and Night is conducive to merit, and hence this knowledge should be acquired;’—this injunction (of acquiring the said knowledge) being implied by the valediction contained in the verse.—(73)