Sahih Muslim 1820
Sahih Muslim · Book 33: The Book on Government · The people follow the Quraish and the Caliphate belongs to the Quraish
It has been narrated on the authority of 'Abdullah that the Messenger of Allah (ﷺ) said:
وَحَدَّثَنَا أَحْمَدُ بْنُ عَبْدِ اللَّهِ بْنِ يُونُسَ ، حَدَّثَنَا عَاصِمُ بْنُ مُحَمَّدِ بْنِ زَيْدٍ ، عَنْ أَبِيهِ ، قَالَ قَالَ عَبْدُ اللَّهِ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " لاَ يَزَالُ هَذَا الأَمْرُ فِي قُرَيْشٍ مَا بَقِيَ مِنَ النَّاسِ اثْنَانِ " .
The Caliphate will remain among the Quraish even if only two persons are left (on the earth),