[Machine] Abu Humaid Al-Ansari came with a container of milk to the Prophet ﷺ during the day when he was in Al-Baqi. The Prophet ﷺ said, "Shouldn't you cover it, even if you do so with a stick?"  

جَاءَ أَبُو حُمَيْدٍ الْأَنْصَارِيُّ بِإِنَاءٍ مِنْ لَبَنٍ نَهَارًا إِلَى النَّبِيِّ ﷺ وَهُوَ بِالْبَقِيعِ فَقَالَ النَّبِيُّ ﷺ أَلَا خَمَّرْتَهُ وَلَوْ أَنْ تَعْرُضَ عَلَيْهِ عُودًا  

I came to Messenger of Allah ﷺ with a cup of milk from Naqi' which had no cover over it, whereupon he said: Why did you not cover it? - even if you had covered it only with a stick. Abu Humaid said that he had been ordered that waterskins be tied during the night, and the doors be closed during the night. (Using translation from Muslim 2010a)   

أَنَّهُ أَتَى النَّبِيَّ ﷺ بِقَدَحِ لَبَنٍ مِنَ النَّقِيعِ لَيْسَ بِمُخَمَّرٍ فَقَالَ النَّبِيُّ ﷺ لَوْلَا خَمَّرْتَهُ وَلَوْ بِعُودٍ تَعْرُضُهُ قَالَ أَبُو حُمَيْدٍ إِنَّمَا أَمَرَ النَّبِيُّ ﷺ بِالْأَسْقِيَةِ أَنْ تُوكَأَ وَبِالْأَبْوَابِ أَنْ تُغْلَقَ لَيْلًا وَلَمْ يَذْكُرْ زَكَرِيَّا قَوْلَ أَبِي حُمَيْدٍ بِاللَّيْلِ