Jabir reported that a person who was known as Abu Humaid brought for him (the Holy Prophet) a cup of milk from al-Naqi'. Allah's Messenger (ﷺ) said to him:Why did you not cover it even with a wood across it?
وَحَدَّثَنَا عُثْمَانُ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا جَرِيرٌ، عَنِ الأَعْمَشِ، عَنْ أَبِي سُفْيَانَ، وَأَبِي، صَالِحٍ عَنْ جَابِرٍ، قَالَ جَاءَ رَجُلٌ يُقَالُ لَهُ أَبُو حُمَيْدٍ بِقَدَحٍ مِنْ لَبَنٍ مِنَ النَّقِيعِ فَقَالَ لَهُ رَسُولُ اللَّهِ صلى الله عليه وسلم " أَلاَّ خَمَّرْتَهُ وَلَوْ تَعْرُضُ عَلَيْهِ عُودًا " .
Muslim
The Book of Drinks • Hadith 119