One of the last verses to be revealed was the verse on riba, and when the Messenger of Allah ﷺ died, he had not explained it. So avoid riba and any dubious matter.
إِنَّ مِنْ آخِرِ مَا نزِلَ آيَةُ الرِّبَا وَإِنَّ رَسُولَ اللهِ ﷺ تُوُفِّيَوَلَمْ يُفَسِّرْهَا فَدَعُوا الرِّبَا وَالرِّيبَةَ
"The last thing to be revealed was the Verse on usury but the Messenger of Allah ﷺ died before he had explained it to us. So give up usury (interest) and doubtful things."
إِنَّ آخِرَ مَا نَزَلَتْ آيَةُ الرِّبَا وَإِنَّ رَسُولَ اللَّهِ ﷺ قُبِضَ وَلَمْ يُفَسِّرْهَا لَنَا فَدَعُوا الرِّبَا وَالرِّيبَةَ
The last thing to be revealed was the verse on riba, but the Messenger of Allah ﷺ passed away and did not discuss it with us. So give up riba and doubtful things.
قَالَقَالَ عُمَرُ إِنَّ آخِرَ مَا نَزَلَ مِنَ الْقُرْآنِ آيَةُ الرِّبَا وَإِنَّ رَسُولَ اللهِ ﷺ قُبِضَ وَلَمْ يُفَسِّرْهَا فَدَعُوا الرِّبَا وَالرِّيبَةَ
"إِنَّ آخِرَ مَا نَزَلَ مِنَ الْقُرآنِ آيَةُ الرِّبَا، وَإِنَّ رَسُولَ اللهِ ﷺ قُبِضَ وَلَمْ يُفَسِّرْهَا لَنَا، فَدَعُوا الرِّبَا والرِّيبَةَ".