حَدَّثَنَا إِسْمَاعِيلُ، عَنِ ابْنِ أَبِي عَرُوبَةَ، عَنْ قَتَادَةَ، عَنِ ابْنِ الْمُسَيَّبِ، أَنَّ عُمَرَ
رَضِيَ اللَّهُ عَنْهُ قَالَ: إِنَّ مِنْ آخِرِ مَا أُنْزِلَ آيَةُ الرِّبَا وَإِنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ تُوُفِّيَ وَلَمْ يُفَسِّرْهَا فَدَعُوا الرِّبَا وَالرِّيبَةَ
One of the last verses to be revealed was the verse on riba, and when the Messenger of Allah (sallallahu alayhi wa sallam) died, he had not explained it. So avoid riba and any dubious matter.
Musnad Ahmad 332, Book 2, Musnad `Umar b. al-Khattab (ra), Hadith 255. 1 min read