Narrated Um Al-Fadl:

that the people were in doubt whether the Prophet was fasting on the Day of 'Arafat or not, so a (wooden) drinking vessel full of milk was sent to him, and he drank it.

حَدَّثَنِي عَمْرُو بْنُ عَبَّاسٍ، حَدَّثَنَا عَبْدُ الرَّحْمَنِ، حَدَّثَنَا سُفْيَانُ، عَنْ سَالِمٍ أَبِي النَّضْرِ، عَنْ عُمَيْرٍ، مَوْلَى أُمِّ الْفَضْلِ عَنْ أُمِّ الْفَضْلِ، أَنَّهُمْ شَكُّوا فِي صَوْمِ النَّبِيِّ ﷺ يَوْمَ عَرَفَةَ، فَبُعِثَ إِلَيْهِ بِقَدَحٍ مِنْ لَبَنٍ فَشَرِبَهُ.