Sahih Bukhari, Chapter: Oppressions (Al-Mazalim)

A drink (milk mixed with water) was brought to Allah's Apostle (SAW) who drank some of it. A boy was sitting to his right, and some old men to his left. Allah's Apostle (SAW) said to the boy, "Do you allow me to give the rest of the drink to these people?" The boy said, "O Allah's Apostle (SAW)! I will not give preference to anyone over me to drink the rest of it from which you have drunk." Allah's Apostle (SAW) then handed the bowl (of drink) to the boy. (See Hadith No. 547).