Volume 1, Book 12, Number 742:
Narrated Abu Wa’il:
A man came to Ibn Mas’ud and said, “I recited the Mufassal (Suras) at night in one Rak’a.” Ibn
Mas’ud said, “This recitation is (too quick) like the recitation of poetry. I know the identical Suras
which the Prophet used to recite in pairs.” Ibn Mas’ud then mentioned 20 Mufassal Suras including
two Suras from the family of (i.e. those verses which begin with) AL, HA, MIM (which the Prophet
used to recite) in each Rak’a.