Sunan Ibn Majah, Volume 2, Book 7, Hadith 1662 (DarusSalam) ⓘ
It was narrated that ‘Aishah said: “Hamzah Al-Aslami asked the Messenger of Allah: ‘I am fasting, should I fast while traveling?’ The Messenger of Allah said: ‘If you wish, then fast, and if you wish, then break your fast.’”
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا عَبْدُ اللَّهِ بْنُ نُمَيْرٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، قَالَتْ سَأَلَ حَمْزَةُ الأَسْلَمِيُّ رَسُولَ اللَّهِ ـ صلى الله عليه وسلم ـ فَقَالَ إِنِّي أَصُومُ أَفَأَصُومُ فِي السَّفَرِ فَقَالَ ـ صلى الله عليه وسلم ـ " إِنْ شِئْتَ فَصُمْ وَإِنْ شِئْتَ فَأَفْطِرْ " .
also referenced under: Hadith 1662 (Reference) & Book 7, Hadith 1731 (In-Book)