Sayyiduna Sa'id bin Zayd (may Allah be pleased with him) narrates from the Prophet (peace and blessings be upon him) that he (peace and blessings be upon him) said: "Among the worst forms of usury (riba) is that a man unjustly attacks the honour of a Muslim with his tongue. And this kinship (rahim) is a branch derived from al-Rahman; whoever severs it, Allah will forbid Paradise to him."
Hadith Referenceالمعجم الكبير للطبراني / العشرة / 354