Sahih al-Bukhari Book 87, Hadith 9
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).
The Prophet (ﷺ) said during Hajjat-al-Wada`, "Let the people be quiet and listen to me. After me, do not become disbelievers, by striking (cutting) the necks of one another."
The Prophet (ﷺ) said, "The biggest of Al-Ka`ba'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 a false witness."