While I was in the company of ʿAbdullah bin ʿUmar 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 ʿIsha 'prayers together and said, " I saw the Prophet ﷺ delaying the Maghrib prayer to offer it along with the ʿIsha' when he was in a hurry on a journey."  

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 ﷺ إِذَا جَدَّ بِهِ السَّيْرُ أَخَّرَ الْمَغْرِبَ وَجَمَعَ بَيْنَهُمَا  

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). (Using translation from Bukhārī 1805)   

عَنْ صَفِيَّةَ شِدَّةَ وَجَعٍ فَأَسْرَعَ السَّيْرَ حَتَّى كَانَ بَعْدَ غُرُوبِ الشَّفَقِ ثُمَّ نَزَلَ فَصَلَّى الْمَغْرِبَ وَالْعَتَمَةَ جَمَعَ بَيْنَهُمَا وَقَالَ إِنِّي رَأَيْتُ رَسُولَ اللهِ ﷺ إِذَا جَدَّ بِهِ السَّيْرُ أَخَّرَ الْمَغْرِبَ وَجَمَعَ بَيْنَهُمَا