The Book of the Times (of Prayer)
6/46. Chapter:
Situations During Which It Is Permissible To Combine Two Prayers
Sunan an-Nasai
أَخْبَرَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، عَنْ مَالِكٍ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ إِذَا جَدَّ بِهِ السَّيْرُ جَمَعَ بَيْنَ الْمَغْرِبِ وَالْعِشَاءِ .
It was narrated from Ibn 'Umar that if the Messenger of Allah (ﷺ) was in a hurry to travel, he would combine Maghrib and 'Isha'.
Reference : Sunan an-Nasa'i 598In-book reference : Book 6, Hadith 105English translation : Vol. 1, Book 6, Hadith 599