Sahih Bukhari Volume 7, Book 69, Hadith Number 524.

Narrated By Sahl bin Sad : Allah’s Apostle was offered something to drink. He drank of it while on his right was a boy and on his left were some elderly people. He said to the boy, “May I give these (elderly) people first?” The boy said, “By Allah, O Allah’s Apostle! I will not give up my share from you to somebody else.” On that Allah’s Apostle placed the cup in the hand of that boy.