Musnad Abu Ya'la al-Mawsili 129:36

Wahb ibn Baqiyyah narrated to us, Khalid informed us, from Humayd, from Anas: That Umm Sulaym took his hand upon the arrival of the Messenger of Allah (may Allah bless him and grant him peace) in Medina and said, "O Messenger of Allah, this is Anas, and he is a young boy who can write." Anas said: I served him for nine years, and he never said to me regarding anything I had done, "Why did you do this?" or "How poorly you have done."