Sahih Muslim 4799
صحيح مسلم#4799Sahihوَحَدَّثَنِي وَهْبُ بْنُ بَقِيَّةَ الْوَاسِطِيُّ، حَدَّثَنَا خَالِدُ بْنُ عَبْدِ اللَّهِ، عَنِ الْجُرَيْرِيِّ، عَنْ أَبِي، نَضْرَةَ عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " إِذَا بُويِعَ لِخَلِيفَتَيْنِ فَاقْتُلُوا الآخَرَ مِنْهُمَا " .
It has been narrated on the authority of Aba Sa'id al-Khudri that the Messenger of Allah (ﷺ) said:When oath of allegiance has been taken for two caliphs, kill the one for whom the oath was taken later
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
Every narration in Sahih Muslim is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 33:96