Alqamah and al-Aswad both narrate from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) that a man came to him and said: "I recite the Mufassal surahs in a single rak'ah." He said: "Do you rattle it off quickly like poetry, and scatter it like worthless talk? The Prophet (peace and blessings be upon him) would recite two similar surahs in a single rak'ah." Such as al-Rahman [Surah al-Rahman: 1] and al-Najm [Surah al-Najm: 1] in one rak'ah; "The Hour has drawn near" [Surah al-Qamar: 1] and al-Haqqah [Surah al-Haqqah: 1] in one rak'ah; al-Tur [Surah al-Tur: 1] and al-Dhariyat [Surah al-Dhariyat: 1] in one rak'ah; "When the Event occurs" [Surah al-Waqi'ah: 1] and "Nun. By the pen" [Surah al-Qalam: 1] in one rak'ah; "About what are they asking one another?" [Surah al-Naba': 1] and al-Mursalat [Surah al-Mursalat: 1] in one rak'ah; and al-Dukhan [Surah al-Dukhan: 1] and "When the sun is wrapped up" [Surah al-Takwir: 1] in one rak'ah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4691