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.  

أَنَّ حَمْزَةَ الأَسْلَمِيَّ سَأَلَ النَّبِيَّ ﷺ فَقَالَ يَا رَسُولَ اللَّهِ إِنِّي رَجُلٌ أَسْرُدُ الصَّوْمَ أَفَأَصُومُ فِي السَّفَرِ قَالَ صُمْ إِنْ شِئْتَ وَأَفْطِرْ إِنْ شِئْتَ  

I said: Messenger of Allah. I am a master of mounts and I use them ! I myself travel on them and I rent them. This month, that is, Ramadan, happend to come to me (while I am on a journey), and I find myself strong enough (to fast) as I am young, and I find that it is easier for me to fast than to postpone it, and i becomes debt due from me. Does it bring me more reward, Messenger of Allah, if I fast, or if I break ? He replied: Whichever you like, Hamzah.  

قُلْتُ يَا رَسُولَ اللَّهِ إِنِّي صَاحِبُ ظَهْرٍ أُعَالِجُهُ أُسَافِرُ عَلَيْهِ وَأَكْرِيهِ وَإِنَّهُ رُبَّمَا صَادَفَنِي هَذَا الشَّهْرُ يَعْنِي رَمَضَانَ وَأَنَا أَجِدُ الْقُوَّةَ وَأَنَا شَابٌّ وَأَجِدُ بِأَنْ أَصُومَ يَا رَسُولَ اللَّهِ أَهْوَنَ عَلَىَّ مِنْ أَنْ أُؤَخِّرَهُ فَيَكُونَ دَيْنًا أَفَأَصُومُ يَا رَسُولَ اللَّهِ أَعْظَمُ لأَجْرِي أَوْ أُفْطِرُ قَالَ أَىُّ ذَلِكَ شِئْتَ يَا حَمْزَةُ  

The Prophet ﷺ left Medina for Mecca till he reached 'Usfan, He then called for a vessel (of water). It was raised to his mouth to show it to the people, and that was in Ramadan. Ibn 'Abbas used to say: The Prophet ﷺ fasted and he broke his fast. He who likes may fast and he who likes may break.  

خَرَجَ النَّبِيُّ ﷺ مِنَ الْمَدِينَةِ إِلَى مَكَّةَ حَتَّى بَلَغَ عُسْفَانَ ثُمَّ دَعَا بِإِنَاءٍ فَرَفَعَهُ إِلَى فِيهِ لِيُرِيَهُ النَّاسَ وَذَلِكَ فِي رَمَضَانَ فَكَانَ ابْنُ عَبَّاسٍ يَقُولُ قَدْ صَامَ النَّبِيُّ ﷺ وَأَفْطَرَ فَمَنْ شَاءَ صَامَ وَمَنْ شَاءَ أَفْطَرَ  

We travelled along with the Prophet ﷺ during Ramadan. Some of us were fasting and other broke their fast. Those who fasted did not find fault with those who broke, and those who broke their fast did not find fault with those who fasted.  

سَافَرْنَا مَعَ رَسُولِ اللَّهِ ﷺ فِي رَمَضَانَ فَصَامَ بَعْضُنَا وَأَفْطَرَ بَعْضُنَا فَلَمْ يَعِبِ الصَّائِمُ عَلَى الْمُفْطِرِ وَلاَ الْمُفْطِرُ عَلَى الصَّائِمِ  

I came to Abu Sa'id al-Khudri while he was giving his legal opinion to the people who bent down on him. So I waited to see hi when he was alone. When he became alone, I asked him about keeping fast while travelling. He said: we went out along with the Prophet ﷺ in Ramadan in the year of conquest of Mecca. The Messenger of Allah ﷺ fasted and we fasted until he reached a certain stage. He said: You have come near your enemy; the breaking of fast will bring you more strength. Then morning came when some of us fasted and other broke their fast. He (Abu Sa'id al-Khudri) said: We then proceeded and alighted at a stage. He said: You are going to attack your enemy tomorrow morning ; breaking the fast will bring you more strength ; so break your fast (i.e. do not keep fast). This resolution (of breaking the fast) took place (due to the announcement) from the Messenger of Allah ﷺ. Abu Sa'id said: Then I found myself keeping fast along with the Prophet ﷺ before and after that.  

أَتَيْتُ أَبَا سَعِيدٍ الْخُدْرِيَّ وَهُوَ يُفْتِي النَّاسَ وَهُمْ مُكِبُّونَ عَلَيْهِ فَانْتَظَرْتُ خَلْوَتَهُ فَلَمَّا خَلاَ سَأَلْتُهُ عَنْ صِيَامِ رَمَضَانَ فِي السَّفَرِ فَقَالَ خَرَجْنَا مَعَ النَّبِيِّ ﷺ فِي رَمَضَانَ عَامَ الْفَتْحِ فَكَانَ رَسُولُ اللَّهِ ﷺ يَصُومُ وَنَصُومُ حَتَّى بَلَغَ مَنْزِلاً مِنَ الْمَنَازِلِ فَقَالَ إِنَّكُمْ قَدْ دَنَوْتُمْ مِنْ عَدُوِّكُمْ وَالْفِطْرُ أَقْوَى لَكُمْ فَأَصْبَحْنَا مِنَّا الصَّائِمُ وَمِنَّا الْمُفْطِرُ قَالَ ثُمَّ سِرْنَا فَنَزَلْنَا مَنْزِلاً فَقَالَ إِنَّكُمْ تُصَبِّحُونَ عَدُوَّكُمْ وَالْفِطْرُ أَقْوَى لَكُمْ فَأَفْطِرُوا فَكَانَتْ عَزِيمَةً مِنْ رَسُولِ اللَّهِ ﷺ قَالَ أَبُو سَعِيدٍ ثُمَّ لَقَدْ رَأَيْتُنِي أَصُومُ مَعَ النَّبِيِّ ﷺ قَبْلَ ذَلِكَ وَبَعْدَ ذَلِكَ