Ibn 'Abbas reported that the Messenger of Allah (ﷺ) combined the prayers as he set on a journey in the expedition to Tabuk. He combined the noon prayer with the afternoon prayer and the sunset prayer with the 'Isha' prayer. Sa'id (one of the rawis) said to Ibn 'Abbas: What prompted him to do this? He said: He wanted that his Ummah should not be put to (unnecessary) hardship.
Source: sunnah.com
Other translations
Arabic
وَحَدَّثَنَا يَحْيَى بْنُ حَبِيبٍ الْحَارِثِيُّ، حَدَّثَنَا خَالِدٌ، - يَعْنِي ابْنَ الْحَارِثِ - حَدَّثَنَا قُرَّةُ، حَدَّثَنَا أَبُو الزُّبَيْرِ، حَدَّثَنَا سَعِيدُ بْنُ جُبَيْرٍ، حَدَّثَنَا ابْنُ عَبَّاسٍ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم جَمَعَ بَيْنَ الصَّلاَةِ فِي سَفْرَةٍ سَافَرَهَا فِي غَزْوَةِ تَبُوكَ فَجَمَعَ بَيْنَ الظُّهْرِ وَالْعَصْرِ وَالْمَغْرِبِ وَالْعِشَاءِ . قَالَ سَعِيدٌ فَقُلْتُ لاِبْنِ عَبَّاسٍ مَا حَمَلَهُ عَلَى ذَلِكَ قَالَ أَرَادَ أَنْ لاَ يُحْرِجَ أُمَّتَهُ .
sunnah.com