Sahih Bukhari
Drinks
Volume: 007 / Book Number: 069 / Hadith Number: 523
Narrated Anas bin Malik:
Milk mixed with water was brought to Allah's Apostle while a bedouin was on his right and Abu Bakr was on his left. He drank (of it) and then gave (it) to the bedouin and said, 'The right" "The right (first)."