Full Sharh — Riyad as-Salihin 81
وعن سهل بن سعد رضى الله عنه أن رسول الله صلى الله عليه وسلم أتى بشراب، فشرب منه وعن يمينه غلام، وعن يساره أشياخ، فقال للغلام: "أتأذن لي أن أعطى هؤلاء.؟" فقال الغلام: لا والله ، لا أوثر بنصيبي منك أحدا، فتله رسول الله صلى الله عليه وسلم في يده.((متفق عليه))
English Translation
Sahl bin Sa'd (May Allah be pleased with him) reported:: A drink was brought to the Messenger of Allah (ﷺ) and he drank (some) from it. On his right was a boy and on his left were some elderly people. He (ﷺ) said to the boy, "Would you permit me to give rest of this drink to these on my left?" The boy said: "O Messenger of Allah, I would certainly not give preference to anyone in anything that might come to me from you." So he (ﷺ) handed over the rest of the drink to him..
Source
Riyad as-Salihin(رياض الصالحين)
The Book About the Etiquette of Eating
Hadith Number
81