Musnad Ahmad 652:13

Abu Ahmad narrated to us, Fatar narrated to us, Abu al-Duha narrated to us, he said: I heard al-Nu'man ibn Bashir saying: My father took me to the Messenger of Allah, may Allah bless him and grant him peace, meaning to have him bear witness to a gift he was giving me. He said: "Do you have any children other than him?" He said: "Yes." He said: "Then treat them equally."