Silsilat al-Ahadith al-Sahihah

It is narrated from Sayyiduna Abdullah bin Hanzalah Rahib (may Allah be pleased with him) that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever knowingly consumes one dirham of usury, in the sight of Allah, (this crime) is more severe than committing adultery thirty-six times."

Sayyiduna Bara’ bin ‘Azib (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: “Usury has seventy degrees, the least of which (in sin) is equivalent to a man committing adultery with his own mother.” And the greatest usury, that is, excess, is that a person violates the honor of his brother.”