Bhagavad Gita Chapter 2 Verse 69

yā niśā sarvabhūtānāṃ tasyāṃ jāgarti saṃyamī
yasyāṃ jāgrati bhūtāni sā niśā paśyato muneḥ

That which is night to all beings, in that the self-controlled man keeps awake; where all beings are awake, that is the night for the Sage (MUNI) who sees.

yā = what; niśā = is night; sarva = all; bhūtānāṃ = of living entities; tasyāṃ = in that; jāgarti = is wakeful; saṃyamī = the self-controlled; yasyāṃ = in which; jāgrati = are awake; bhūtāni = all beings; sā = that is; niśā = night; paśyataḥ = for the introspective; muneḥ = sage.;