Narrated Um Al-Fadl bint Al Harith: On the day of `Arafat, some people who were with me, differed about the fasting of the Prophet (ﷺ) (p.b.u.h) some said that he was fasting while others said that he was not fasting. So I sent a bowl full of milk to him while he was riding his camel, and he drank that milk.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ، عَنْ مَالِكٍ، عَنْ أَبِي النَّضْرِ، عَنْ عُمَيْرٍ، مَوْلَى عَبْدِ اللَّهِ بْنِ الْعَبَّاسِ عَنْ أُمِّ الْفَضْلِ بِنْتِ الْحَارِثِ، أَنَّ نَاسًا، اخْتَلَفُوا عِنْدَهَا يَوْمَ عَرَفَةَ فِي صَوْمِ النَّبِيِّ صلى الله عليه وسلم فَقَالَ بَعْضُهُمْ هُوَ صَائِمٌ. وَقَالَ بَعْضُهُمْ لَيْسَ بِصَائِمٍ. فَأَرْسَلَتْ إِلَيْهِ بِقَدَحِ لَبَنٍ وَهْوَ وَاقِفٌ عَلَى بَعِيرِهِ فَشَرِبَهُ.
sunnah.com