Sahih Muslim , Book 33, Hadith 4 (In-Book) ⓘ
It has been narrated on the authority of 'Abdullah that the Messenger of Allah said: The Caliphate will remain among the Quraish even if only two persons are left (on the earth),
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 " .
also referenced under: Hadith 1820 (Reference) & Book 20, Hadith 4476 (USC-MSA)