We were with Messenger of Allah ﷺ and he asked for water. A person said: Messenger of Allah, may we not give you Nabidh to drink? He (the Holy Prophet) said: Yes (you may). He (the narrator) said: Then that person went out speedily and brought a cup containing Nabidh, whereupon Messenger of Allah ﷺ said: Why did you not cover it? - even if it is with a wood. He said that then he drank it.  

كُنَّا مَعَ رَسُولِ اللَّهِ ﷺ فَاسْتَسْقَى فَقَالَ رَجُلٌ يَا رَسُولَ اللَّهِ أَلاَ نَسْقِيكَ نَبِيذًا فَقَالَ بَلَى قَالَ فَخَرَجَ الرَّجُلُ يَسْعَى فَجَاءَ بِقَدَحٍ فِيهِ نَبِيذٌ فَقَالَ رَسُولُ اللَّهِ ﷺ أَلاَّ خَمَّرْتَهُ وَلَوْ تَعْرُضُ عَلَيْهِ عُودًا قَالَ فَشَرِبَ  

We were with Prophet ﷺ and he asked for something to drink. A man from the company asked: Should we not give you nabidh (drink made from dates) to drink ? He replied : Yes . The man went quickly and bought a cup of nabidh. The Messenger of Allah ﷺ said: Why did you not cover it up even by putting a piece of wood on it ? Abu Dawud said: Al-Asma'i's version has: "You put it on it..."  

كُنَّا مَعَ النَّبِيِّ ﷺ فَاسْتَسْقَى فَقَالَ رَجُلٌ مِنَ الْقَوْمِ أَلاَ نَسْقِيكَ نَبِيذًا قَالَ بَلَى قَالَ فَخَرَجَ الرَّجُلُ يَشْتَدُّ فَجَاءَ بِقَدَحٍ فِيهِ نَبِيذٌ فَقَالَ النَّبِيُّ ﷺ أَلاَّ خَمَّرْتَهُ وَلَوْ أَنْ تَعْرِضَ عَلَيْهِ عُودًا