Sahih Bukhari
Virtues of the Quran
Volume: 006 / Book Number: 061 / Hadith Number: 554
Narrated Said bid Jubair:
Those Suras which you people call the Mufassal, are the Muhkam. And Ibn 'Abbas said, "Allah's Apostle died when I was a boy of ten years, and I had learnt the Muhkam (of the Qur'an).