Cover Your Drink
Abu Humaid (an Ansari man) came from An-Naqi carrying a cup of milk to the Prophet (sal Allahu alaihi wa sallam). The Prophet (sal Allahu alaihi wa sallam) said: “Will you not cover it even by placing a stick across it?” [Sahih Bukhari]
Drinks should always be kept covered. They should be covered while transporting and when stored. If they are left open insects could fall inside or take a drink depositing their germs in them.
This is only the obvious advantage of keeping drinks covered. There must be other benefits to be accrued, for the Prophet (sal Allahu alaihi wa sallam) said to cover with a stick if one could find nothing else, and it is obvious that covering with a stick can’t keep insects away.
Allah (subhana wa ta’ala) alone knows what the innumerable other benefits are because of which He has recommended that we cover drinks when not drinking from them.