Abu Dawud Book 20, Hadith Number 3725.

Chapter : Covering vessels.

Narated By Jabir : We were with the Prophet (may peace be upon him) 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 brought a cup of nabidh. The Apostle of Allah (may peace be upon him) 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…”