Sahih Bukhari Volume 003, Book 031, Hadith Number 209.

Narated By Um Al-Fadl bint Al-Harith : "While the people were with me on the day of 'Arafat they differed as to whether the Prophet was fasting or not; some said that he was fasting while others said that he was not fasting. So, I sent to him a bowl full of milk while he was riding over his camel and he drank it."