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 ‏"‏ ‏.‏

It has been narrated on the authority of 'Abdullah that the Messenger of Allah (PBUH) said: The Caliphate will remain among the Quraish even if only two persons are left (on the earth), Translation Not Available

Book reference: Sahih Muslim Book 33 Hadith 4476
Web reference: Sahih Muslim Book 20 Hadith 1820