Sahih al-Bukhari, Hadith 7140 ⓘ
Narrated Ibn `Umar: Allah's Messenger said, "This matter (caliphate) will remain with the Quraish even if only two of them were still existing."
حَدَّثَنَا أَحْمَدُ بْنُ يُونُسَ، حَدَّثَنَا عَاصِمُ بْنُ مُحَمَّدٍ، سَمِعْتُ أَبِي يَقُولُ، قَالَ ابْنُ عُمَرَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " لاَ يَزَالُ الأَمْرُ فِي قُرَيْشٍ مَا بَقِيَ مِنْهُمُ اثْنَانِ " .
also referenced under: Book 93, Hadith 4 (In-Book) & Volume 9, Book 89, Hadith 254 (USC-MSA)