Musnad Ahmad 25:742

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from Abu Bishr, from Sa‘id ibn Jubayr, from Ibn ‘Abbas, who said: "The Messenger of Allah (may Allah bless him and grant him peace) died while I was ten years old, and I was circumcised, and I had read the *Muhkam* of the Qur’an." He said: So I said to Abu Bishr, "What is the *Muhkam*?" He said: "The *Mufassal*."