It is narrated from Sayyidah Aishah (may Allah be pleased with her) that Hamzah bin Amr al-Aslami (may Allah be pleased with him) asked the Prophet (peace and blessings be upon him) and said: "O Messenger of Allah, I am a man who fasts continuously; should I fast while travelling?" He (peace and blessings be upon him) said: "Fast if you wish, and break your fast if you wish."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 2957