Sahih Muslim Book - 1, Hadith - 401

و حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ وَأَبُو كُرَيْبٍ وَاللَّفْظُ لَأَبِي كُرَيْبٍ قَالَا حَدَّثَنَا أَبُو مُعَاوِيَةَ حَدَّثَنَا الْأَعْمَشُ عَنْ إِبْرَاهِيمَ التَّيْمِيِّ عَنْ أَبِيهِ عَنْ أَبِي ذَرٍّ قَالَ دَخَلْتُ الْمَسْجِدَ وَرَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ جَالِسٌ فَلَمَّا غَابَتْ الشَّمْسُ قَالَ يَا أَبَا ذَرٍّ هَلْ تَدْرِي أَيْنَ تَذْهَبُ هَذِهِ الشَّمْسُ ؟ قَالَ قُلْتُ اللَّهُ وَرَسُولُهُ أَعْلَمُ قَالَ فَإِنَّهَا تَذْهَبُ فَتَسْتَأْذِنُ فِي السُّجُودِ فَيُؤْذَنُ لَهَا وَكَأَنَّهَا قَدْ قِيلَ لَهَا ارْجِعِي مِنْ حَيْثُ جِئْتِ فَتَطْلُعُ مِنْ مَغْرِبِهَا قَالَ ثُمَّ قَرَأَ فِي قِرَاءَةِ عَبْدِ اللَّهِ وَذَلِكَ مُسْتَقَرٌّ لَهَا.

It was narrated that Abu Dharr said: "I entered the Masjid and the Messenger of Allah (s.a.w) was sitting there. When the sun disappeared he said: 'O Abu Dharr, do you know where this sun goes?' I said: 'Allah and His Messenger know best.' He said: 'It goes and asks for permission to prostrate, and permission is granted to it, and it is as if it will be told: Return from where you came, and it will rise from its place of setting.'"