I was with Ibn ʿUmar on the way to Mecca, and he got the news that Safiya bint Abu Ubaid was seriously ill. So, he hastened his pace, and when the twilight disappeared, he dismounted and offered the Maghrib and ʿIsha' prayers together. Then he said, "I saw that whenever the Prophet ﷺ had to hasten when traveling, he would delay the Maghrib prayer and join them together (i.e. offer the Maghrib and the ʿIsha prayers together).  

عَنْ صَفِيَّةَ بِنْتِ أَبِي عُبَيْدٍ شِدَّةُ وَجَعٍ فَأَسْرَعَ السَّيْرَ حَتَّى كَانَ بَعْدَ غُرُوبِ الشَّفَقِ نَزَلَ فَصَلَّى الْمَغْرِبَ وَالْعَتَمَةَ جَمَعَ بَيْنَهُمَا ثُمَّ قَالَ إِنِّي رَأَيْتُ النَّبِيَّ ﷺ إِذَا جَدَّ بِهِ السَّيْرُ أَخَّرَ الْمَغْرِبَ وَجَمَعَ بَيْنَهُمَا