A man said in the presence of Abdullah, "I recited the Mufassal in a single rakah."Abdullah replied, "That is reciting as hastily as one rattles off poetry. I know the pairings that the Messenger of Allah ﷺ used to recite together." He then mentioned twenty surahs from the Mufassal, paired two by two in each rakah.
أخبرنا إسمعيل بن مسعود قال حدثنا خالد قال حدثنا شعبة عن عمرو بن مرة قال سمعت
قال رجل عند عبد الله قرأت المفصل في ركعة قال هذا كهذ الشعر لقد عرفت النظائر التي كان رسول الله ﷺ يقرن بينهن فذكر عشرين سورة من المفصل سورتين سورتين في ركعة
Bukhari transmitted it in the Book of Adhan, Chapter on Combining Two Surahs in One Rakat, etc., hadith 775, and Muslim in the Book of the Prayer of Travelers, Chapter on Reciting the Quran Slowly and Avoiding Rushing, etc., hadith 279/822, from the hadith of Shubah, with this wording, and it is found in Al-Kubra, hadith 1077.