A man came to him and said, "I recited the entire Mufassal in a single rakah tonight."He replied, "That is the rapid recitation of poetry. But the Messenger of Allah ﷺ used to recite the matched pairs, twenty surahs from the Mufassal beginning with the Ha-Mim chapters."
أخبرنا عمرو بن منصور قال حدثنا عبد الله بن رجاء قال أنبأنا إسرائيل عن أبي حصين عن يحيى بن وثاب عن مسروق
وأتاه رجل فقال إني قرأت الليلة المفصل في ركعة فقال هذا كهذ الشعر لكن رسول الله ﷺ كان يقرأ النظائر عشرين سورة من المفصل من آل حم
Its isnad is sahih. Tabarani narrated it in Al-Kabir: 10/40 from the hadith of Abdullah bin Raja, with this wording, in abridged form. It is also in Al-Kubra, no. 1078. Bukhari narrated it, no. 5043, 4996, 775, and Muslim, no. 822, through the route of Shaqiq, from Ibn Masud, with similar wording.