Yahya related to me from Malik from Hisham ibn Urwa from hisfather that Hamza ibn Amr al-Aslami once said to the Messenger ofAllah, may Allah bless him and grant him peace, "Messenger of Allah, Iam a man who fasts. Can I fast when travelling?" The Messenger ofAllah, may Allah bless him and grant him peace, said, "If you want youcan fast, and if you want you can break the fast." (IT)
USC-MSA web (English) reference: Book 18, Hadith 24 (IT)
Arabic reference (IT): Book 18, Hadith 658 (IT)