"The Messenger of Allah went out to Makkah, and he fasted until he came to 'Usfan. Then he called for a cup and drank." (One of the narrators) Shubah said: "(That was) in Ramadan. Ibn 'Abbas used to say: 'Whoever wants to fast, may fast, and whoever wants to break may break his fast."'
Sunan an-Nasa'i Book 22, Hadith 201