Musnad Ahmad 25:1266

Hushaym narrated to us, Abu Bishr informed us, from Sa’id ibn Jubayr, from Ibn Abbas, who said: "I gathered the *Muhkam* during the time of the Messenger of Allah, peace and blessings of Allah be upon him, and the Prophet, peace and blessings of Allah be upon him, passed away while I was ten years of age." He said: So I said to him: "And what is the *Muhkam*?" He said: "The *Mufassal*."