Sahih Muslim Book 1, Hadith Number 161.

Chapter : Major sins and the gravest among these.

It is reported on the authority of Abu Huraira that the Messenger of Allah (may peace be upon him) observed: Avoid the seven noxious things. It was said (by the hearers): What are they, Messenger of Allah? He (the Holy Prophet) replied: Associating anything with Allah, magic, killing of one whom God has declared inviolate without a just cause, consuming the property of an orphan, and consuming of usury, turning back when the army advances, and slandering chaste women who are believers, but unwary.