Sahih al-Bukhari 1106
Sahih al-Bukhari · Book 18: Shortening the Prayers (At-Taqseer) · To offer Maghrib and "Isha" prayers together on a journey
Narrated Salim's father:
حَدَّثَنَا عَلِيُّ بْنُ عَبْدِ اللَّهِ ، قَالَ حَدَّثَنَا سُفْيَانُ ، قَالَ سَمِعْتُ الزُّهْرِيَّ ، عَنْ سَالِمٍ ، عَنْ أَبِيهِ ، قَالَ كَانَ النَّبِيُّ صلى الله عليه وسلم يَجْمَعُ بَيْنَ الْمَغْرِبِ وَالْعِشَاءِ إِذَا جَدَّ بِهِ السَّيْرُ.
The Prophet (ﷺ) used to offer the Maghrib and `Isha' prayers together whenever he was in a hurry on a journey.