Sahih al-Bukhari Book 87, Hadith 8
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, "After me (i.e. after my death), do not become disbelievers, by striking (cutting) the necks of one another.
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).