Usury

Source: http://hadithoftheday.com/

Narrated Abu Juhaifa: The Prophet (peace be upon him) forbade the use of the price of blood and the price of a dog, the one who takes (eats) usury the one who gives usury, the woman who practices tattooing and the woman who gets herself tattooed.
Sahih Al-Bukhari – Book 72 Hadith 829

Narrated Abu Huraira: The Prophet (peace be upon him) said, “Avoid the seven great destructive sins.” They (the people) asked, “O Allah’s Apostle! What are they?” He said, “To join partners in worship with Allah; to practice sorcery; to kill the life which Allah has forbidden except for a just cause (according to Islamic law); to eat up usury (Riba), to eat up the property of an orphan; to give one’s back to the enemy and fleeing from the battlefield at the time of fighting and to accuse chaste women who never even think of anything touching chastity and are good believers.”
Sahih Al-Bukhari – Book 82 Hadith 840

Narrated Abu Burda: When I came to Medina, I met Abdullah bin Salam. He said, “Will you come to me so that I may serve you with Sawiq (i.e. powdered barley) and dates, and let you enter a (blessed) house that in which The Prophet (peace be upon him) entered?” Then he added, “You are in a country where the practice of Riba (i.e. usury) is prevalent; so if somebody owes you something and he sends you a present of a load of chopped straw or a load of barley or a load of provender then do not take it, as it is Riba.”
Sahih Al-Bukhari – Book 58 Hadith 159