(the wife of the Prophet) Hamza bin ʿAmr Al-Aslami asked the Prophet, "Should I fast while traveling?" The Prophet ﷺ replied, "You may fast if you wish, and you may not fast if you wish."  

عَنْ عَائِشَةَ ؓ زَوْجِ النَّبِيِّ ﷺ أَنَّ حَمْزَةَ بْنَ عَمْرٍو الأَسْلَمِيَّ قَالَ لِلنَّبِيِّ ﷺ أَأَصُومُ فِي السَّفَرِ وَكَانَ كَثِيرَ الصِّيَامِ فَقَالَ إِنْ شِئْتَ فَصُمْ وَإِنْ شِئْتَ فَأَفْطِرْ  

We set out with Messenger of Allah ﷺ on one of his journeys on a very hot day, and it was so hot that one had to put his hand over his head because of the severity of heat. None of us was fasting except the Prophet and Ibn Rawaha.  

خَرَجْنَا مَعَ النَّبِيِّ ﷺ فِي بَعْضِ أَسْفَارِهِ فِي يَوْمٍ حَارٍّ حَتَّى يَضَعَ الرَّجُلُ يَدَهُ عَلَى رَأْسِهِ مِنْ شِدَّةِ الْحَرِّ وَمَا فِينَا صَائِمٌ إِلاَّ مَا كَانَ مِنَ النَّبِيِّ ﷺ وَابْنِ رَوَاحَةَ