Abu Dawud Book 20, Hadith Number 3717.
Chapter : When should the supplier drink.
Narated By Anas b. Malik : The Prophet (may peace be upon him) was brought milk that was mixed with water. A nomad Arab was on his right and Abu Bakr was on his left. He himself drank and gave it to the nomad Arab, and said: He who is on the right, then he who is on his right.