Abu Wa'il said that a man came to Sayyiduna Abdullah (may Allah be pleased with him) and said: Last night I recited the whole of the Mufassal in one rak'ah. He said: Scattering it like bad dates and rattling through it hastily like poetry (is that prayer)? I know the surahs of similar length and theme which the Messenger of Allah (peace and blessings be upon him) used to combine, two by two, in one rak'ah.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9824