Sahih Muslim 1913
صحيح مسلم#1913SahihAbu Wa'il reported:A person came to 'Abdullah b. Mas'ud and said: I recited all the mufassal surahs in one rak'ah during the night. 'Abdullah said: You must have recited hastily like the recitation of poetry. 'Abdullah said: I remember well the manner in which the Messenger of Allah (ﷺ) used to combine them, and he then mentioned twenty of the mufassal surahs, and (their combinations in) two in every rak'ah
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih Muslim is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 6:341