Narrated Anas bin Malik (Radi-Allahu 'anhu):
The Prophet (Sallallahu 'Alaihi Wa Sallam) said, "The biggest of Al-Kaba'ir
(the great sins) are (1) to join others as partners in worship with Allah,
(2) to murder a human being, (3) to be undutiful to one's parents (4) and
to make a false statement," or said, "to give false witness."
Bukhari Vol. 9 : No. 10