Musnad Ahmad 26:60

Abu Mu’awiyah narrated to us, Al-A’mash narrated to us, from Shaqiq ibn Salamah, who said: A man from the tribe of Bajilah, called Nuhayk ibn Sinan, came to Abdullah and said: "O Abu Abd al-Rahman, how do you recite this verse? Do you find it with a ya or an alif: {min ma’in ghayri asin} [Muhammad: 15]?" Abdullah said to him: "Have you counted all of the Quran except for this?" He said: "I recite the Mufassal in one rak'ah." Abdullah said: "Like the reciting of poetry? Indeed, part of performing prayer well is the bowing and the prostration. There will be people who recite the Quran, but it will not pass beyond their collarbones. However, if it is recited and it takes root in the heart, it benefits. I know the pairs that the Messenger of Allah, peace and blessings of Allah be upon him, used to recite, two surahs in one rak'ah." He said: Then he stood up and entered. Then Alqamah came and entered upon him. He said: We said to him: "Ask him for us about the pairs that the Messenger of Allah, peace and blessings of Allah be upon him, used to recite, two surahs in one rak'ah." He said: So he entered and asked him, then he came out to us and said: "Twenty surahs from the beginning of the Mufassal," according to the arrangement of Abdullah.