It is narrated from Sayyidah Umm al-Fadl bint al-Harith (may Allah be pleased with her) that some people, in her presence on the day of Arafah, differed about whether the Messenger of Allah (peace and blessings be upon him) was fasting. Some said he was fasting, and some said he was not fasting. So she sent a cup of milk to him (peace and blessings be upon him) while he (peace and blessings be upon him) was halted on his camel, and he (peace and blessings be upon him) drank that milk at Arafah.
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 21497