Sahih Bukhari Volume 3, Book 48, Hadith Number 821.

Narated By Anas : The Prophet 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.”