Abu Amr al-Shaybani narrates: Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) had earlier given a concession regarding sarf (currency exchange with excess on one side), and also in the issue that if a man marries a woman and she dies before the marriage is consummated, he may marry her mother. Then he came to Madinah and, it seems, met Sayyiduna Umar (may Allah be pleased with him) and retracted (his opinion). Then he went to the money-changers and forbade them from that.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 8544