Narrated `Abdullah bin `Amr:
The Prophet (ﷺ) said, "Al-Ka`ba'ir (the biggest sins) are: To join others (as partners) in worship with Allah, to be undutiful to one's parents," or said, "to take a false oath." (The sub-narrator, Shu`ba is not sure) Mu`adh said: Shu`ba said, "Al-Ka`ba'ir (the biggest sins) are: (1) Joining others as partners in worship with Allah, (2) to take a false oath (3) and to be undutiful to one's parents," or said, "to murder (someone unlawfully).
