Abdullah bin Abbas reported,
Regarding 
"seven of the oft-repeated", he said this refers to the seven long surahs.
Nasai 917
Hasanأخبرنا علي بن حجر قال حدثنا شريك عن أبي إسحق عن سعيد بن جبير
عن ابن عباس في قوله
عز وجل {سبعا من المثاني} قال السبع الطول
النسائي 917حسن
Contents
Reference
Commentary
Ayat
Collection
Sunan Nasai Sughra
Book
Commencement
Chapter
Tafsir of the saying of Allah , "And We have certainly given you seven of the often repeated verses and the great Quran"
, "And We have certainly given you seven of the often repeated verses and the great Quran"Numbering
Darussalam 917
Details
Collection
Sunan Nasai Sughra
Book
Commencement
Chapter
Tafsir of the saying of Allah , "And We have certainly given you seven of the often repeated verses and the great Quran"
, "And We have certainly given you seven of the often repeated verses and the great Quran"Numbering
Darussalam 917
Ayat
Reference
Nasai916
Commentary
Darussalam
hasanIt is also in Kubra, hadith 988. Abu Ishaq Sabi was corroborated by Israil and Amash. Ibn Jareer, 14/35.