It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with him), he says: I had memorized the Muhkam Surahs during the time of the Messenger of Allah (peace and blessings be upon him), while I was ten years old. I (Saeed bin Jubair) asked him: What is meant by Muhkam? He said: The Mufassal Surahs.