Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) says: The Mufassal surahs were revealed in Makkah, and for a period of time we kept reciting only them; nothing besides them had been revealed.
Al-Tabarani recorded it in al-Mu'jam al-Awsat; its chain contains a narrator, Hudayj bin Mu'awiyah, whom Ahmad and others declared thiqah (trustworthy), while a group declared him da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب التفسير / 11621