From Sahih Bukhari (Hadith 1988):
Narrated Um Al-Fadl bint Al-Harith:"While the people were with me on the day of `Arafat they differed as to whether the Prophet (ﷺ) 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
Reference: Bukhari 1988