Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: The surahs which you call "Mufassalat" are in fact "Muhkamat." At the time of the Prophet's (peace be upon him) passing, I was ten years old, and by that time I had recited all the Muhkamat.
Hadith Referenceمسند احمد / ومن مسند بني هاشم / 2283