Sayyidah Umm al-Fadl bint al-Harith (may Allah be pleased with her) said that some people differed on the day of Arafah about the Messenger of Allah (peace and blessings be upon him): some said that he was fasting and some said that he was not. So she sent him a cup of milk while he (peace and blessings be upon him) was mounted on a camel, and he (peace and blessings be upon him) drank it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9470