Abu al-Fayd (may Allah have mercy on him) said: Maslamah bin Abd al-Malik addressed us and said: Do not fast Ramadan while travelling; whoever fasts must make it up. Abu al-Fayd said: Then I met Abu Qirsafah Wathilah bin al-Asqa' (may Allah be pleased with him) and asked him, and he said: If you fasted while travelling, then fasted, then fasted, you would not make it up.
Hadith Referenceالمعجم الكبير للطبراني / باب الواو / 18341