Musannaf Ibn Abi Shayba 3:6350

Waki’ narrated to us, he said: Al-A’mash narrated to us, from Abu Wa’il, he said: A man from Banu Bajilah, called Nuhayk ibn Sinan, came to Ibn Mas’ud and said: "O Abu Abd al-Rahman, how do you recite this letter? Do you find it with a ya or an alif: 'min ma'in ghayri yasin' (from water not stagnant) or 'min ma'in ghayri asin'?" Abdullah said to him: "Have you counted all the Quran except for this?" He said: "I recite the Mufassal in one rak'ah." He said: "This is like the reciting of poetry. Verily, there are people who recite the Quran, but it does not pass beyond their collarbones. But if the Quran settles in the heart and becomes firmly established, it benefits. The best of prayer is the bowing and the prostration." He said: And Abdullah said: "I indeed know the pairs (surahs) that the Messenger of Allah, peace and blessings of Allah be upon him, used to recite together."