Musnad Abu Ya'la al-Mawsili 147:15

Sarij ibn Yunus narrated to us, Ismail ibn Ibrahim narrated to us, from Ayyub, from Amr ibn Sa'id, from Anas, who said: "I have not seen anyone more merciful to children than the Messenger of Allah, may Allah bless him and grant him peace." He then mentioned the like of it.