Narrated Aslam:While I was in the company of `Abdullah bin `Umar on the way to Mecca, he received the news of the severe illness of Safiya bint Abi Ubaid (i.e. his wife), so he proceeded at greater speed, and when the twilight disappeared, he dismounted and offered the Maghrib and `Isha 'prayers together and said, " I saw the Prophet (ﷺ) delaying the Maghrib prayer to offer it along with the `Isha' when he was in a hurry on a journey."
حَدَّثَنَا سَعِيدُ بْنُ أَبِي مَرْيَمَ، أَخْبَرَنَا مُحَمَّدُ بْنُ جَعْفَرٍ، قَالَ أَخْبَرَنِي زَيْدٌ ـ هُوَ ابْنُ أَسْلَمَ ـ عَنْ أَبِيهِ، قَالَ كُنْتُ مَعَ عَبْدِ اللَّهِ بْنِ عُمَرَ ـ رضى الله عنهما ـ بِطَرِيقِ مَكَّةَ، فَبَلَغَهُ عَنْ صَفِيَّةَ بِنْتِ أَبِي عُبَيْدٍ شِدَّةُ وَجَعٍ، فَأَسْرَعَ السَّيْرَ حَتَّى إِذَا كَانَ بَعْدَ غُرُوبِ الشَّفَقِ، ثُمَّ نَزَلَ فَصَلَّى الْمَغْرِبَ وَالْعَتَمَةَ، يَجْمَعُ بَيْنَهُمَا، وَقَالَ إِنِّي رَأَيْتُ النَّبِيَّ صلى الله عليه وسلم إِذَا جَدَّ بِهِ السَّيْرُ أَخَّرَ الْمَغْرِبَ وَجَمَعَ بَيْنَهُمَا.
Bukhari
Fighting for the Cause of Allah (Jihaad) • Hadith 209