Sahih Bukhari Volume 2, Book 26, Hadith Number 723.

Narated By Um Al-Fadl bint Al Harith : On the day of ‘Arafat, some people who were with me, differed about the fasting of the Prophet (p.b.u.h) some said that he was fasting while others said that he was not fasting. So I sent a bowl full of milk to him while he was riding his camel, and he drank that milk.