Sahih Muslim Book 23, Hadith Number 5000.

Chapter : Command pertaining to the covering of vessels, and tightening (the mouths) of waterskins, etc.

Jabir b. ‘Abdullah reported Allah’s Messenger (may peace be upon him) as saying: Cover the vessels and tie the water-skin, for there is a night in a year when pestilence descends, and it does not pass an uncovered vessel or an untied water-skin but some of that pestilence descending into it.