سنن أبي داود

Narrated Qaza'ah:

I came to Abu Sa'id al-Khudri while he was giving his legal opinion to the people who bent down on him. So I waited to see hi when he was alone. When he became alone, I asked him about keeping fast while travelling. He said: we went out along with the Prophet (ﷺ) in Ramadan in the year of conquest of Mecca. The Messenger of Allah (ﷺ) fasted and we fasted until he reached a certain stage. He said: You have come near your enemy; the breaking of fast will bring you more strength. Then morning came when some of us fasted and other broke their fast. He (Abu Sa'id al-Khudri) said: We then proceeded and alighted at a stage. He said: You are going to attack your enemy tomorrow morning ; breaking the fast will bring you more strength ; so break your fast (i.e. do not keep fast). This resolution (of breaking the fast) took place (due to the announcement) from the Messenger of Allah (ﷺ).

Abu Sa'id said: Then I found myself keeping fast along with the Prophet (ﷺ) before and after that.