It is narrated from Sayyidah Aishah (may Allah be pleased with her) that Hamzah bin Amr (may Allah be pleased with him) said: "O Messenger of Allah, I used to fast continuously, so should I fast while travelling?" He (peace and blessings be upon him) said: "If you wish, fast; and if you wish, break your fast."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 2963