Abu Humaid brought a cup of mix from a place called Al-Naqi. Messenger of Allah ﷺ said to him, "Will you not cover it, even by placing a stick across its" (Using translation from Bukhārī 5605)   

جَاءَ أَبُو حُمَيْدٍ إِلَى رَسُولِ اللهِ ﷺ بِلَبَنٍ فِي قَدَحٍ فَقَالَ لَهُ رَسُولُ اللهِ ﷺ «أَلَا خَمَّرْتَهُ؟ وَلَوْ أَنْ تَعْرِضَ عَلَيْهِ عُودًا»