Abu Wa'il (may Allah have mercy on him) narrated that a person came to Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) and said, "I recited the Surahs of Mufassal in one rak'ah at night." He (Ibn Mas'ud) said, "Did you recite them quickly like poetry is recited? I know those similar Surahs which the Prophet (peace and blessings of Allah be upon him) used to recite together. He mentioned twenty Surahs of Mufassal, two Surahs in each rak'ah."
Hadith Referenceاللؤلؤ والمرجان / كتاب صلاة المسافرين وقصرها / 470
Hadith Gradingمحدثین:«صحیح»
Hadith Takhrij«صحیح، أخرجه البخاري في: 10 كتاب الأذان: 106 باب الجمع بين السورتين في الركعة»
Brief Explanation
Sayyiduna Ibn Abbas (radi Allahu anhuma) said that by “Mufassal” is meant the “Muhkam” (clear and decisive) surahs, that is, the surahs from Surah al-Fath to the end of the Qur’an. They are called “Mufassal” because there are many separations/distinctions in them through “Bismillah” and the like. By “Naza’ir” are meant those surahs in which meanings such as admonitions, advice, rulings, and stories are mentioned. In these, there is correspondence in the number of verses. Among them are: ar-Rahman, an-Najm, Iqtarabat (al-Qamar) and al-Haqqah, adh-Dhariyat and at-Tur, al-Waqi‘ah and Nun (al-Qalam), Sa’ala Sa’il (al-Ma‘arij) and an-Nazi‘at, Wail lil-Mutaffifin and ‘Abasa, al-Muddathir and al-Muzzammil, Hal Ata (al-Insan) and La Uqsimu, ‘Amma Yatasa’alun and al-Mursalat, Idha ash-Shamsu Kuwwirat and ad-Dukhan.