Tafseer Ibn Kathir of AL ANBIYAA' [33]

وَهُوَ الَّذِي خَلَقَ اللَّيْلَ وَالنَّهَارَ وَالشَّمْسَ وَالْقَمَرَ كُلٌّ فِي فَلَكٍ يَسْبَحُونَ

And it is He who created the night and the day and the sun and the moon; all [heavenly bodies] in an orbit are swimming.