Abd al-Rahman bin Abdullah bin Mas'ud narrates from his father (Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him)) that the Prophet (peace and blessings be upon him) "cursed the one who takes usury (riba), the one who pays it, and its two witnesses — or one witness — and its scribe."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10469