(Annajm) 53 : 1
بِسْمِ اللَّهِ الرَّحْمَٰنِ الرَّحِيمِ وَالنَّجْمِ إِذَا هَوَىٰ

And the star, when it sets.

By swearing the visible phenomenon of star and thereby the dawn appearing, Allah says.