Hamzat al-Aslami asked the Prophet ﷺ: Messenger of Allah, I am a man who keeps perpetual fast, may I fast while on a journey? He replied: Fast if you like, or break your fast if you like. (Using translation from Abū Dāʾūd 2402)
أَنَّ حَمْزَةَ بْنَ عَمْرٍو الْأَسْلَمِيَّ سَأَلَ النَّبِيَّ ﷺ فَقَالَ يَا رَسُولَ اللهِ إِنِّي رَجُلٌ أَسْرُدُ الصَّوْمَ أَفَأَصُومُ فِي السَّفَرِ؟ فَقَالَ «صُمْ إِنْ شِئْتَ وَأَفْطِرْ إِنْ شِئْتَ»