Sahih Muslim Book - 6, Hadith - 1627

وَحَدَّثَنِى أَبُو الطَّاهِرِ وَعَمْرُو بْنُ سَوَّادٍ قَالاَ أَخْبَرَنَا ابْنُ وَهْبٍ حَدَّثَنِى جَابِرُ بْنُ إِسْمَاعِيلَ عَنْ عُقَيْلٍ عَنِ ابْنِ شِهَابٍ عَنْ أَنَسٍ عَنِ النَّبِىِّ -صلى الله عليه وسلم- إِذَا عَجِلَ عَلَيْهِ السَّفَرُ يُؤَخِّرُ الظُّهْرَ إِلَى أَوَّلِ وَقْتِ الْعَصْرِ فَيَجْمَعُ بَيْنَهُمَا وَيُؤَخِّرُ الْمَغْرِبَ حَتَّى يَجْمَعَ بَيْنَهَا وَبَيْنَ الْعِشَاءِ حِينَ يَغِيبُ الشَّفَقُ.

It was narrated from Anas that if the Prophet (s.a.w) was in a hurry while traveling, he would delay Zuhr until the beginning of the time for 'Asr and then join them, and he would delay Maghrib until he joined it with 'Isha', when the twilight had disappeared.