Kuraib, the freed slave of Ibn 'Abbas (Allah be pleased with him), reported from Maimuna, the wife of the Messenger of Allah (ﷺ), that people had doubt about the fasting of Allah's Messenger (ﷺ) on the day of 'Arafa. Maimuna sent him a cup of milk and he was halting at a place and he drank it and the people were seeing him.
Source: sunnah.com
Other translations
Arabic
وَحَدَّثَنِي هَارُونُ بْنُ سَعِيدٍ الأَيْلِيُّ، حَدَّثَنَا ابْنُ وَهْبٍ، أَخْبَرَنِي عَمْرٌو، عَنْ بُكَيْرِ بْنِ، الأَشَجِّ عَنْ كُرَيْبٍ، مَوْلَى ابْنِ عَبَّاسٍ - رضى الله عنهما - عَنْ مَيْمُونَةَ، زَوْجِ النَّبِيِّ صلى الله عليه وسلم أَنَّهَا قَالَتْ إِنَّ النَّاسَ شَكُّوا فِي صِيَامِ رَسُولِ اللَّهِ صلى الله عليه وسلم يَوْمَ عَرَفَةَ فَأَرْسَلَتْ إِلَيْهِ مَيْمُونَةُ بِحِلاَبِ اللَّبَنِ وَهُوَ وَاقِفٌ فِي الْمَوْقِفِ فَشَرِبَ مِنْهُ وَالنَّاسُ يَنْظُرُونَ إِلَيْهِ .
sunnah.com