Abu hurairah (Radi Allahu anhu)
Said that the prophet (Sallallahu Alaihi wasallam) said: Avoid the 7 destructive sins. The people enquired; O messenger of Allah what are they?
He said:
1. To join others in worship along with Allah
2. To practice sorcery
3. To kill a person whom Allah had forbidden except for a just cause
4. To eat up riba (interest/usury)
5. To eat up an orphan's wealth
6. To turn back on the enemy and flee from the battlefield while fighting
7. To accuse a chaste woman,who never even think of anything and is a true believer.

SAHIH AL-BUKHARI VOL.4 HADITH 28