Muwatta Malik, Book 20, Hadith 836 (In-Book) ⓘ

Yahya related to me from Malik from Abu'n Nadr, the mawla of Umar ibn Ubaydullah, from Umayr, the mawla of Abdullah ibn Abbas, from Umm al-Fadl bint al-Harith, that she was present when some people were arguing on the day of Arafa about whether the Messenger of Allah, may Allah bless him and grant him peace, was fasting or not. Some of them said he was fasting, and some of them said he was not. So she sent a bowl of milk to him while his camel was standing still and he drank.

حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ أَبِي النَّضْرِ، مَوْلَى عُمَرَ بْنِ عُبَيْدِ اللَّهِ عَنْ عُمَيْرٍ، مَوْلَى عَبْدِ اللَّهِ بْنِ عَبَّاسٍ عَنْ أُمِّ الْفَضْلِ بِنْتِ الْحَارِثِ، أَنَّ نَاسًا، تَمَارَوْا عِنْدَهَا يَوْمَ عَرَفَةَ فِي صِيَامِ رَسُولِ اللَّهِ صلى الله عليه وسلم فَقَالَ بَعْضُهُمْ هُوَ صَائِمٌ وَقَالَ بَعْضُهُمْ لَيْسَ بِصَائِمٍ فَأَرْسَلْتُ إِلَيْهِ بِقَدَحِ لَبَنٍ وَهُوَ وَاقِفٌ عَلَى بَعِيرِهِ فَشَرِبَ ‏.‏