Sunan an-Nasa'i, Book 6, Hadith 606 (In-Book) ⓘ
It was narrated that Ibn 'Umar said: "If the Messenger of Allah was in a hurry to travel, or some emergency arose, he would combine Maghrib and 'Isha'."
أَخْبَرَنَا إِسْحَاقُ بْنُ إِبْرَاهِيمَ، قَالَ أَنْبَأَنَا عَبْدُ الرَّزَّاقِ، قَالَ حَدَّثَنَا مَعْمَرٌ، عَنْ مُوسَى بْنِ عُقْبَةَ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم إِذَا جَدَّ بِهِ السَّيْرُ أَوْ حَزَبَهُ أَمْرٌ جَمَعَ بَيْنَ الْمَغْرِبِ وَالْعِشَاءِ .
also referenced under: Volume 1, Book 6, Hadith 600 (DarusSalam)