Sahih Bukhari Volume 4, Book 51, Hadith Number 29.
Narated By Anas : When Allah’s Apostle came to Medina; he did not have any servant. Abu Talha (Anas’ step-father) took me to Allah’s Apostle and said, “O Allah’s Apostle! Anas is a wise boy, so let him serve you.” So, I served him at home and on journeys. If I did anything, he never asked me why I did it, and if I refrained from doing anything, he never asked me why I refrained from doing it.