Some people were disputing in her presence on the day of Arafah about whether the Messenger of Allah ﷺ was fasting. Some said he was fasting, while others said he was not. So she sent him a cup of milk while he was standing on his camel at Arafah, and he drank it.
حدثنا القعنبي عن مالك عن أبي النضر عن عمير مولى عبد الله بن عباس
أن ناسا تماروا عندها يوم عرفة في صوم رسول الله ﷺ فقال بعضهم هو صائم وقال بعضهم ليس بصائم فأرسلت إليه بقدح لبن وهو واقف على بعيره بعرفة فشرب
Bukhari narrated it in the Book of Fasting, chapter "The Fast of the Day of Arafah," Hadith 1988, and Muslim in the Book of Fasting, chapter "The Recommendation of Breaking the Fast for the Pilgrim at Arafat on the Day of Arafah," Hadith 1123, both from the hadith of Malik through this chain, and it is found in Muwatta (Yahya): 1/375.