It is narrated from Sayyiduna Sahl bin Sa'd (may Allah be pleased with him) that a cup of water was brought to the Prophet (peace and blessings be upon him), and he (peace and blessings be upon him) drank from it. On his right was a young boy, the youngest of the people, and on his left were elderly men. When he (peace and blessings be upon him) had finished drinking, he said: "O boy, do you permit me to give it to the elders?" The boy said: I will not prefer anyone over myself in what is left over from you. So the Messenger of Allah (peace and blessings be upon him) placed the cup in that boy's hand.
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5869