It was narrated that Ibn 'Abbas said:

"The Messenger of Allah (ﷺ) set out at nightfall, then stopped to camp at the end of the night, and he did not wake up until the sun had risen or had partly risen. He did not pray until the sun had risen (fully), then he prayed, and that was the 'middle prayer' (Salat Al-Wusta)."

أَخْبَرَنَا أَبُو عَاصِمٍ، قَالَ حَدَّثَنَا حَبَّانُ بْنُ هِلاَلٍ، حَدَّثَنَا حَبِيبٌ، عَنْ عَمْرِو بْنِ هَرِمٍ، عَنْ جَابِرِ بْنِ زَيْدٍ، عَنِ ابْنِ عَبَّاسٍ، قَالَ أَدْلَجَ رَسُولُ اللَّهِ صلى الله عليه وسلم ثُمَّ عَرَّسَ فَلَمْ يَسْتَيْقِظْ حَتَّى طَلَعَتِ الشَّمْسُ أَوْ بَعْضُهَا فَلَمْ يُصَلِّ حَتَّى ارْتَفَعَتِ الشَّمْسُ فَصَلَّى وَهِيَ صَلاَةُ الْوُسْطَى ‏.‏