Nafi' reported that when Ibn 'Umar was in a state of hurry on a journey, he combined the sunset and 'Isha' prayers after the twilight had disappeared, and he would say that when the Messenger of Allah ﷺ was in a state of hurry on a journey, he combined the sunset and 'Isha' prayers.
أَنْ يَغِيبَ الشَّفَقُ وَيَقُولُ إِنَّ رَسُولَ اللَّهِ ﷺ كَانَ إِذَا جَدَّ بِهِ السَّيْرُ جَمَعَ بَيْنَ الْمَغْرِبِ وَالْعِشَاءِ