Surah Ar-Ra'd, Ayah 15

All that are in the heavens and on earth submit themselves in prostration to Allah alone. A believer and disbeliever are equal in this, except that a believer submits and prostrates to Him willingly, while a disbeliever unwillingly submits even though his natural disposition dictates that he should do so willingly. The shadow of every creation that has a shadow submits to Him at the beginning and at the end of the day.

And unto Allah falls in prostration whoever is in the heavens and the earth, willingly or unwillingly, and so do their shadows in the mornings and in the afternoons (15)

Everything prostrates unto Allah

Allah affirms His might and power, for He has full control over everything, and everything is subservient to Him. Therefore, everything, including the believers, prostrate to Allah willingly, while the disbelievers do so unwillingly,

وَظِلَالُهُم بِالْغُدُوِّ

(and so do their shadows in the mornings), in the beginning of the days,

وَالْآصَالِ

(and in the afternoons.) towards the end of the days. Allah said in another Ayah,

أَوَلَمْ يَرَوْا إِلَىٰ مَا خَلَقَ اللَّهُ مِن شَيْءٍ يَتَفَيَّأُ ظِلَالُهُ

(Have they not observed things that Allah has created: (how) their shadows incline.)[16:48]