Narrated Anas (Radi-Allahu ‘anhu):
The Prophet (Sallallahu ‘Alaihi Wa Sallam) was asked about the great sins
He said, “They are:
(1) To join others in worship with Allah,
(2) To be undutiful to one’s parents.
(3) To kill a person (which Allah has forbidden to kill) (i.e. to commit the crime of murdering).
(4) And to give a false witness.”

Bukhari Vol. 3 : No. 821