Musnad Abu Ya'la al-Mawsili 150:150

'Abd al-A'la narrated to us, from 'Umar ibn 'Ali, [who] narrated to us, from Hisham ibn 'Urwah, from his father, from 'Aishah, that Hamzah ibn 'Amr al-Aslami asked the Messenger of Allah, may Allah bless him and grant him peace, and said: "I travel, so should I fast?" He said: "If you wish, then fast, and if you wish, then break your fast."