Sunan An-Nasa'i

It was narrated that Ibn 'Abbas said:""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