Mishkat al-Masabih 2830
‘Umar b. al-Khattab said:
The last verse to be sent down was that on usury (Al-Qur’an 2:275) but God's Messenger was taken without having expounded it to us; so leave aside usury and whatever is doubtful.

 Ibn Majah and Darimi transmitted it.
وَعَنْ عُمَرَ بْنِ الْخَطَّابِ رَضِيَ اللَّهُ عَنْهُ إِنَّ آخِرَ مَا نَزَلَتْ آيَةُ الرِّبَا وَإِنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قُبِضَ وَلَمْ يُفَسِّرْهَا لَنَا فَدَعُوا الرِّبَا وَالرِّيبَةَ. رَوَاهُ ابْن مَاجَه والدارمي