The Book of Drinks (Kitab Al-Ashriba)
Muslim :: Book 23 : Hadith 5032
Anas b. Malik reported that there was brought to Allah's Messenger (may peace be upon him) a cup of milk mixed with water, while there was on his right a desert Arab and on his left Abu Bakr. He (the Holy Prophet) drank; he then gave it to the desert Arab and said: (Give to one) who is on the right, then again who is on the right.