(We have given thee seven of the oft-repeated (verses) and the great Qur'an…) [15:87].
Al-Husayn ibn al-Fadl said: “Seven caravans, belonging to the Jews of Qurayzah and al-Nadir from Busrah and Adhri'at, arrived in the same day. They brought different kinds of linen, stuff of perfumes and jewels and sea stuff. The Muslims said: 'Had these riches been ours, we would have derived some strength from them and spent them in the way of Allah'. And so Allah, exalted is He, revealed this verse. He said: 'I have given you seven verses which are better than these seven caravans'. The authenticity of this report is evidenced by what Allah, exalted is He, says after this verse (Strain not thine eyes toward that which We cause some wedded pairs among them to enjoin) [15:88]”.
Asbab Al-Nuzul by Al-Wahidi , trans. Mokrane Guezzou