On the day of 'Arafah some people near her argued whether the Messenger of Allah (ﷺ) was fasting, some saying that he was, and others saying that he was not. I, therefore, sent him a cup of milk while he was observing the halt at 'Arafah on his camel, and he drank it.
Sunan Abi Dawud Book 14, Hadith 129