Hadithcore
Mishkat al-Masabih, 1339

Ibn ‘Abbas said that God’s Messenger used to combine the noon and the afternoon prayer while travelling, and also to combine the sunset and the evening prayer. Bukhari transmitted it.

وَعَنِ ابْنِ عَبَّاسٍ قَالَ: كَانَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يَجْمَعُ بَين الظُّهْرِ وَالْعَصْر إِذَا كَانَ عَلَى ظَهْرِ سَيْرٍ وَيجمع بَين الْمغرب وَالْعشَاء. رَوَاهُ البُخَارِيّ

References1 variant
In-Book Reference
Book 4, Hadith 746