Musnad Ahmad 32:1731

Hassan ibn Musa narrated to us, Salam—meaning Ibn Miskin—narrated to us, from Thabit, who said: I heard Anas ibn Malik saying: "I served the Messenger of Allah, may Allah bless him and grant him peace, for ten years. He never once said 'Uff' to me, nor did he ever say to me, 'Why did you do such and such?'"