The Caliphate will remain among the Quraish even if only two persons are left (on the earth), (Using translation from Muslim 1820)
قَالَ رَسُولُ اللهِ ﷺ لَا يَزَالُ هَذَا الْأَمْرُ فِي قُرَيْشٍ مَا بَقِيَ مِنَ النَّاسِ اثْنَانِ قَالَ وَحَرَّكَ إِصْبَعَيْهِ يَلْوِيهِمَا هَكَذَا