Mishkat al-Masabih 1344
Mu'adh b.Jabal said that on the expedition to Tabuk,* if the sun had passed the meridian before the Prophet moved off he combined the noon and the afternoon prayer, but if he moved off before the sun had passed the meridian he delayed the noon prayer till he halted for the afternoon prayer. He acted similarly regarding the sunset prayer:
if the sun set before he moved off he combined the sunset and the evening prayer, but if he moved off before sunset he delayed the sunset prayer till he halted for the evening prayer and then combined them. 

*In 19 AH.

Abu Dawud transmitted it.
وَعَنْ مُعَاذِ بْنِ جَبَلٍ قَالَ: كَانَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فِي غَزْوَةِ تَبُوكَ: إِذَا زَاغَتِ الشَّمْسُ قَبْلَ أَنْ يَرْتَحِلَ جَمَعَ بَيْنَ الظُّهْرِ وَالْعَصْرِ وَإِنِ ارْتَحَلَ قَبْلَ أَنْ تَزِيغَ الشَّمْسُ أَخَّرَ الظُّهْرَ حَتَّى يَنْزِلَ لِلْعَصْرِ وَفِي الْمَغْرِبِ مِثْلَ ذَلِكَ إِذَا غَابَتِ الشَّمْسُ قَبْلَ أَنْ يَرْتَحِلَ جَمَعَ بَيْنَ الْمَغْرِبِ وَالْعِشَاءِ وَإِنِ ارْتَحَلَ قَبْلَ أَنْ تَغِيبَ الشَّمْسُ أَخَّرَ الْمَغْرِبَ حَتَّى يَنْزِلَ لِلْعِشَاءِ ثُمَّ يَجْمَعُ بَيْنَهُمَا. رَوَاهُ أَبُو دَاوُد وَالتِّرْمِذِيّ